My Boxer puppy seems to have a problem. He is 8 months old and he has agression towards other submissive dogs. We have another dog and they play all day and he has no problems with her at all. However, when we take him to the dog park and take him off the leash, he displays agression toward any smaller dog and any dog who shows submission to him. Wih the bigger dogs he is fine. With the small dogs, as soon as they cower or roll on their backs he pins them down and starts growling at them and I am sure if we did not take him away he would bite them. What is wrong with him and what can we do?