Our dogs gets real aggressive towards un-neutered dogs. All the dogs appears to be larger than him. Our dog is neutered. This happens at our dog park. He can play with any dog at the the park that wants to run with him but if he i guess smells something he runs over to the dog and confronts him face to face, growling, showing his teeth and a want to take him down in a fight. It is an un-neutered dog. He has gotten really bad in the past week. This behavior was not present say a month ago. he started this in the last few weeks. we must of missed something. now we do not know what to do. he has to go to the park to release his energy.