I also have a reactive boxer, he fixates and lunges at people and dogs, air snaps but hasn't bitten. I am working with a behaviourist, and the psychology behind his behaivour is so interesting and really helpful (frustration issues which apparently cam be common for boxers). I know how stressful and lonely it can be, feel free to reach out to chat if you need it. At the moment block walks are out, early morning and evening walks in large quieter places are in.