Black German Shepherd pup aggression
I have joined this forum to ask for help and any input would be appreciated.
We have black, working dog German Shepherd named Titan. He is 13 weeks old. We got him at 6 weeks since we didn't know better at the time. We got him from a backyard breeder. On our way back pup got hungry and while my partner was feeding him, pup must have thought that my partner was taking away food and bit him. That said, it was enough to draw blood but not too much. That said he is not food agressive now and does not guard his stuff. When we got him home, we had other dog Jack Rusell Terrier that attacked him and we called a trainer that said to let them sort it out. We listened to the advice and then it happened again. We called the trainer and he said that Jack Rusell needs to be rehomed. He lives now in my mothet in law's house. Titan has been good with kids, some dominant behavior that we are fixing. He is well trained. He sits before he gets his food, fetches the ball, plays soccer, lies down, comes, walks well on a lead, play with his toys and so on. His biting and chewing is now minimal. He is a very smart dog but very dominant. This brings me to my other issue, today my partner was fixing a lead into the seat belt so that the dog was put. The dog started growling at him and air snapping. This was definitely agression, he didn't want to be moved.
Now I am wondering whether this agression is a long term problem and whether I need to rehome the dog to someone more knowledgeable.
Thank you for any help that you can offer.