I am trying to teach my 13 week old Boxer mix "Rocky" how to give me paw. Earlier I believe he was doing it, but out of maybe 30 or more times doing it with him he has only done it twice. I say "Gimme Paw." and grab his paw to show him, then give him a treat, and give him a chance to do it, he's just not getting it! Am I doing something wrong? I don't know why he is not getting it.