How often does he fly? If he is flying a lot when there are people at the club, I would probably discuss it like you have, but if you were established as a model field for a long time, that should be precidence and if he shoots someone down, it would be his responcibility to replace the plane and anything else damaged. If he is shot down, it would still be considered his fault, unless you did it on purpose. I wouldn't suggest that.

If he won't work with you to solve the problem, talk to the county or a lawyer and see what comes out. That could be a dangerous thing if he starts shooting people down because he is mad. Hate people like that, but they are everywhere.