Our dog is a male chihuahua/shih tzu mix, and he is 10 years old. For our family, he is the perfect dog, and he even gets along with most dogs of similar or smaller size. He becomes aggressive with larger dogs though, and barks, kicks, and even tries to attack sometimes, even when the larger dog is being submissive.
We have learned to live with this, but the issue is that my boyfriend has a pit bull mix, and our inability to bring the dogs together is becoming a problem. His dog is extremely friendly and gentle, just large and energetic. Our dogs have never met because I know mine will become aggressive immediately.
How should I proceed? My dog is already very well-trained, except in this one area. Could training of some sort be beneficial at this stage, or is there anything else I can do?