Think of a food that Duke loves. Something like cheese, or chicken, something you can break into small pieces. we will work first on teaching duke to LOVE restraint and vets and he relaxes about the biting. . Get a clicker and prime the click with food. I want you to Click, treat, click treat. so Duke associates the click with the treat and as soon as you click you get a immediate response that Duke turns quickly and looks at you for the food. If he trys to bite you, do not deliver the food with your fingers. put down a small square of tile, or a little bowl... some small item you can use for a show me place to put the food after the click. You can even use one of those fold up bowls that are made of fabric so you can pull the dish out whenever you need it.
If he is food aggressive, don't put your face down or lean toward the bowl. bowl on floor, click and then step in and drop the treat while standing upright and using good body language and back up as you praise him with your voice.
This is part one... basic clicker training because we are going to use a clicker on the next steps. Do read carefully what I said. Do not lean toward him or use your hands to treat at this point if you are afraid he will snap at you or grab your hands. Use a dish on the floor. we can work up to hand treating later.
Try this and text back and let me know if you have any issues, describe his response to the click and treat and tell me what food you choose... game to try? easier to do step by step than type out whole exercise only to change something because of dog response.
PS, german shepherd dogs frequently take quick nips when they are in the brain mode of herding. My shepherd didn't do it with us but did it with our other dogs and he tore a small hole in our doberman with the nipping. he loved her, but the nipping while herding was when he was trying to drive her where he wanted her and she was laughing and running and ignoring her. We can try to override his previous training or his herding behavior which ever it is, but teaching him to associate terrific food tid bits with things he doesnt like.
Picture the dog that doesn't like his paws held. Picture me doing click treat prime, then reach for paw, click treat, then reach for paw touch paw and treat... then reach hold paw and treat, reach and wiggle fingers in paw and treat. Never move on to next step without dog being comfortable with first step. Pick a treat dog really loves.
will write more... DO tell me if you don't feel comfortable with him to try this level and we will come up with something else. I will never tell somebody to buck up and move forward without dog being comfortable. It isn't about tough... it is about staying safe and not creating the situation where you "invite the bite". stay tuned.