We had a problem with a "jumper" too. The normal technique to get a dog to sit is to lift the treat over the dog's head until he sits. That works because a dog's head is higher sitting than standing. Well, if the dog jumps, that technique doesn't really work.
We found that it works to back him into a corner of a room so his bottom's toward the corner; he doesn't really have the space to jump. Then, you can bring the treat over his head until he sits.
Good luck! |