This is not something that will be altered within a couple of sessions, group classes or with a quick fix. Contrary to popular belief, fear aggression or resource guarding cannot be cured, it needs to be managed.
Depending on the issues and the situation we are facing will depend on the overall plan needed to change the dog's view of the problem. After all, the general consensus is that a dog should simply fit into our homes and our lives, right? ......Wrong! The most important thing here is to work out what is the root cause of any aggression or fear and anxiety is, and work together to alter the dog's thought process to be able to alter the behaviour.
Anxiety is not the same as fear however is often a precursor to being fearful.
......Warning....If your dog has got to this stage in their behaviour then this problem will NOT go away. Your companion has likely to have been offering many signs of his or her dislike of a particular situation and feel that they have not been listened to. You need to act now.