Thank you for all of your words of wisdom. In regards to neutering: he is intact only because our trainer suggested that the negatives of neutering outweighed the positives, including the increase in fear and anxiety when testosterone is taken away. Since we have felt that his aggression stems from some kind of fear, it is a major concern of mine that this would irreversibly aggravate his behaviour. We have thought about it though, and the temporary implant is certainly an option.