Call It Off!
No really. I’ve seen them laughing during set up as they look at their course map.
Be that as that may be, you can foil their trapping plans by mastering the ‘call off’. This is a must have skill for every agility dog, and indeed, every dog. It’s like ‘come’ but different. It’s stop doing what you’re doing right now, and come back my way to do something else, or come to me.
Set up three or four obstacles in a clear row, and practice sending your dog ahead through them. Then call your dog between obstacle two and three, and take off running. Jackpot if your dog comes to you instead of taking the next obstacle! Slowly raise the self-reward level of the next obstacle (You may be able to call off a table no problem, but can you call off a jump?) and also raise the value of the treat you use. Make it big and beautiful and wonderful when they come to you off of something they find extremely fun.
If your dog doesn’t come off the next obstacle, you may have to return to on-leash work (please be careful when using leashes on agility courses), move closer, or start your calling off practice with recalls.
Do not call off the same obstacle every time. Do not call off obstacles in every run. You do want your dog to have definite forward motion, but to be listening to you for that one in ten times you call them away from that oh so tempting tunnel.