Our 5 month Aussie boy Riley is being quite bad lately. He has been very "sassy" and will bite us if we try to touch him when he doesn't want to be touched. He growls at my younger siblings when they pet him while he's sleeping (we have made a point of doing that on purpose to try and break that) and at people he doesn't know, he growled at the vet yesterday when all she was doing was touching him, and we are getting very discouraged. We've had a trainer out and she told us to teach him to be "gentle" when he tries biting, and to "leave it" when he takes something he's not supposed to. We've been doing that for at least a month and it has not worked! Before that we tried the puppy yelp, the ignoring him when he does it, etc. The vet said yesterday that when she sees a dog this young come in and do what he did, they usually end up being the kind of dog they have to muzzle when they get older. She suggested an obedience class.. which is a good idea. But what can we do to make him stop biting? Yes, he has broken my skin twice -- once was when I was telling him to "leave it" and he got sassy and started yipping and biting at my hand. The second time was when we were looking at his teeth because he broke one. (Vet says it was a baby tooth.) We are all of us wondering if Riley was such a good choice now. We don't want him to be a bad dog. Telling him a big, firm "NO" only makes him get sassy. I love him and I hate him at the same time.... Any help, input, encouragement, pointers, etc. would be greatly appreciated right now.