Blocking and Advanced Proofing with Barriers

A student recently described how her dog found most of the hides in SDDA Excellent competition, but had a fringe alert. Did she call alert too soon or block her dog’s access to source? If she had asked her dog to check both sides of the vehicle, would he have sat and false alerted just to please her? Maybe, but she’s in good company. Fringe alerts are common in scent detection tests and competition. Fortunately, you can prepare for barriers that block your dog’s path and improve your sourcing (scroll down for video commentary).


Blocking occurs when the handler gets in the dog’s way, impeding them from getting to source. Both humans and objects may block access to odor, leading to fringe alerts, missed hides and failures by timing out. (Timing out means the allotted search time runs out before all hides are found.)

  • Sometimes well-intentioned volunteers, photographers or spectators get in a dog’s way, causing social pressure and unintentional obstruction in confined spaces
  • In one UKC exterior search, the hide was in a crack in the cement on the ground. Most handlers timed out searching all of the distracting cold strollers, statues and objects. They stood over the non-object hide and inadvertently blocked their dogs from finding source.
  • In a novice UKC vehicle search, every dog fringe alerted on the side of a vehicle where strong wind caused odor to pool. The vehicles were on an open plain, with high velocity winds, on a hot, dry day. Even though the official briefing stressed that only the front bumper was in play, all teams alerted on the pool of odor to the side rather than locating the source under the front bumper.

Fringe alerts occur when the dog is in odor, but hasn’t worked it to source (the highest concentration of odor). Odor travels freely, but dogs don’t. This is true when searching any object with 4 sides, but is especially prominent in vehicle searches with wind. The scent plume is frequently carried under the vehicle, but the dog can’t crawl under the vehicle to get to source (it’s a safety fault). If the wind is chaotic, it’s difficult to avoid blocking while the dog chases scent like a whirling ghost in the wind. If strong winds prevail in one general direction, green dogs may get stuck in the pool of odor, rather than working it back to source on the opposite side of the vehicle. In contrast, experienced dogs can learn to independently search all the sides until they find source and indicate accordingly.

When you have a short leash, in an enclosed space, even if it’s clear of odor, inexperienced dogs may not know what to do and default to obedience behaviors if the handler blocks the dog or stands still staring at an object of interest. Some dogs run to a visual objective (like a box or vehicle) and enthusiastically sit or lie down, aiming to please. Handlers can train for these scenarios, helping their dogs to check all sides before calling the alert.

Try setting up one challenge at a time, like the video. To train your dog, you must know where source is (NOT blind searches). Since you know exactly where the hide is, you can offer assistance if it’s required, and reward the dog the instant he’s successful, instead of failing and leaving confused. Properly done, training with barriers can help prevent fringe alerts, and improve your sourcing.

While your dog is learning, hopefully you tried to make it hard for the dog to be wrong, controlling the environment to set your dog up for success. When proofing advanced dogs, aim to fail more in practice! Challenge your dog to work harder to get to source. Show him clearly what is right and what is wrong. Only reward at source, not just “close”. Addressing your weaknesses in practices can help you to succeed when those skills are tested under pressure in blind searches.


So is your dog ready for the challenge, or is he still in the learning phase? How do you know you’re ready for advanced proofing? Consider some prerequisites:

  • Does your dog easily and consistently find source when presented with a stack of boxes with holes 1 inch apart?
  • Is your dog comfortable searching that environment e.g. vehicles, or exteriors? With distractions? On the road?
  • Are you happy with your indication?
  • Do you understand how scent is carried by the wind during vehicle searches so you can help your dog if he’s stymied?

You never want to overface (i.e. overwhelm) your dog, so don’t get greedy and push to finish training by a certain date. Every dog learns at his own pace and impatience to achieve human goals is a shortcut to frustration. Repeated failures cause stress, lower motivation, and should lead to re-evaluating your training plans.

Trust your dog to show you when he’s under stress and pay attention! If you get into trouble, add lots of distance and regroup. Sometimes you think your dog is ready for a challenge and find out he isn’t. Blaming won’t help. Instead, look at failures as helpful information. Notice holes in your training and plan to address them later, one at a time. In today’s training session you have to adapt and train the dog you have on that day, in that environment. Be more rewarding, go back to where you succeeded last time, and ask for help if you don’t know what to do next.

When you are ready for advanced proofing, here are some ideas incorporating barriers and blocking. As always, take what you like and leave the rest.


The featured video above shows a training session with most experienced dog, Boo, and BB (a younger dog that competed once before taking a break to recover from surgery). Here’s what happened:

5 seconds – First, I start the dog so he’s facing the wrong side of the hot box. This sets up potential to false alert on the closest side, instead of finding source between the back side of the box and the cabinets. Boo demonstrates confident, independent sourcing. He’s ready for a challenge. If your dog does not easily identify source in this test, DO NOT MAKE IT HARDER!

11 seconds – Diving right in, I use my body position to mislead my dog and block him from easily getting to source. I kneel at a distraction box filled with masking odor (bed bug scent) when the hot box with nosework scent is behind me. My eyes, shoulders and hand point at the incorrect choice. The food reward is in my open hand on the wrong box to tempt him to fail, and I tap the wrong box, asking my dog to check there. When he fails, my timely feedback and tone of voice communicate that he’s wrong, without making a big deal of it. I encourage and give the dog time to solve the problem, without sacrificing motivation. (You can use a neutral non-reward marker like “oops” if you’ve trained one. I strongly recommend against saying “no” around odor because that can cause a negative association.)

54 seconds – His indication isn’t great, but I reward him for finding source, which is what we’re focussing on in this session. I’ve relaxed my expectations because we’re focussing on blocking in this session and he overcame a difficult challenge. When he is right, there’s a marked difference in what happens: timely praise in my happy voice and high value rewards.  Showing him these dramatic opposites help clarify understanding, without anger. We’re learning as a team.

1 minute – I position a crate and ex-pen to block the path to the hot box and make it easy to fail. Doing this search off leash allows my dog to ignore what I’m doing and independently find source. My dog has to work to get to source and I reward well. This challenge is easier for Boo than ignoring my misleading body language and positioning earlier.

1:23 – Next we search outside, where the fence prevents Boo from getting to the hot box. It’s about 20 feet to the fence door, so my dog needs to travel 40 feet to get to source. When he succeeds, I deliver a chicken breast as the jackpot at source. Don’t be cheap with the rewards when proofing!

1:52  – Shows an easier fence exercise with my less experienced dog, BB. If she wasn’t engaging with me and pulling towards the hot box, I would not have proceeded. (With my 6 month old puppies, we worked solely on engagement and play in this distracting environment.) BB looks to me for guidance because the door is shut, she’s on a short leash and she knows she’s not allowed to jump the fence. I open the door and let her pull me to the hot box. Because she did well, we move on to a more challenging vehicle search with wind that blows the scent plume under the vehicle.

Note that Boo’s indication is a freeze and position is incidental, while BB’s indication is a sit or down. For all of my dogs, my goal is nose pressed to source while indicating (or as close as physically possible), since that tells me the precise location of source.

BB driving ahead with confidence in an exterior search. Photo by Kristy Strunks Photography.

2:07 – I start my dog on the wrong side of the vehicle. BB detects the pool of odor on the passenger side of the vehicle. She pulls strongly under the vehicle, and that would be a safety fault, so I hold her back with the leash. (Taking the direct path under the vehicle to get to source makes sense to dogs, but it is a safety issue so I tighten the leash to prevent her from crawling under.) I’m happy she didn’t offer a fringe alert. (If she had, I would have used my neutral tone of voice to tell her she made a mistake.) I let her work it out independently, pulling me around the vehicle to source. If she was really stumped or appeared discouraged, I would have helped by tapping the other side and asking her to check there. If she failed again, I’d have to reevaluate.

I reward finding source the instant her nose reaches source, since this search was difficult for her. If I waited for a perfect indication, I’d be taking a chance that she might leave the hide without a reward. The reward is the glue that helps keep her at the hide. Then I give extra rewards for indicating with nose pressed at source.

3:14 – Boo searches the same vehicle. It’s an easy search for him. I don’t want every search to be hard! We finish with a fun reward event, tugging his stuffed bird toy.

In conclusion, testing your skills, noticing holes in your training and working through one appropriate challenge at a time can help to build your skills, and your trust in your partner. Don’t endlessly drill to prevent fringe alerts; mix it up. The art of dog training is balancing appropriate challenge with drive to find target odor. Make your praise and rewards worth the effort of proofing barriers and blocking. Try surprising your dog with a short, easy search and quit while he wants more.

Have you failed a search where barriers amped up the difficulty? Which exercises do you use to prevent fringe alerts? Drop us a line in the comments below.

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