Hi, I'm Dr Steve.I wold like to help you with Charlie's problems. I have a few questions to better understand your situation.
Has he always done this? When did this behavior start? Is he and the other dog neutered? how long have you had your other dog? I will check later this evening to see your replies and then I will address your concerns. Thanks for your patience
I am sorry to hear about Charlie's behavior. Unfortunately with him being so aggressive for such a long time, this may be a very difficult behavior to correct. Since he has been aggressive towards people at least to some degree since a puppy, this is not likely to change. I will address things to try towards his recent aggression towards Buster.
When a dog suddenly develops aggression towards another dog, it can be that Charlie is now seeing BUster as a threat. It is very difficult to understand or know why a dog will suddenly do this with another dog , but that is usually the cause. As dogs get older some will develop a fear of losing their position inthe pack hierarchy, even if there is no apparent change in the pecking order. When a dog , in their own mind, feel that their position is being threatened, they often will become the aggressor in an attempt , again , in their mind to show the perceived threat that they are still in control.
This is often displayed in aggression towards the other dog. In my experience the best way to address this is to help reduce the fear or anxiety that the dog ( Charlie in this case) is feeling. THis can be done with a Dog Appeasing Pheromone spray ( DAP ) that helps dogs feel more comfortable or safer in their environment or in their situation. This is a natural Pheromone that mothers produce to help theit pups feel safe.
ANother , possibly more effective option is using an antianxiety medicine. I have has good results with Clomicalm and Reconcile. These are both pills given every day to help reduce anxiety in dogs that may be having increased anxiety for a variety of reasons. THis medicine is available from your vet . It can take 2-4 weeks to see if it is going to help so I have my clients use it for 30 days and if there is no benefit, then they know that it isn't going to help in their specific situation. The only way to know if it is going to help is to try it with Charlie. If this medicine doesn't help there are others that your vet can discuss with you , but I like these two first because they are licensed for use in dogs and the other aren't as of yet. I truly wish you luck because this can be a very difficult situation to correct. I hope this has helped. I will check later to see if you have more questions. This question will remain accessible even after you have rated my answer in case you have more questions or just to give me an update. Good luck and thanks for the questions.
Food aggression is another way that a dog can attempt to show dominance over another dog so this also seems to make sense. I wish you well and good luck.