Hardhatter, there was indeed at least one case of ballistic recovery system killing a Cirrus pilot. However, the guy deployed it in a situation it was never designed for, and had by that time already violated a lot of written and unwritten rules, including flying VFR into IMC.
As to your initial question, I'd propose firing a burst of red flares at the offender. This would serve several purposes at once:
- a red flare is an old and documented way of saying "go away" (just like the flashing red light gun);
- a burst of small flares can be made to look like anti-aircraft fire, exerting a psychological pressure on the pilot;
- if properly designed, such flares could be made with very small (but non-zero) destructive power, so that if the pilot fails to heed the warning, the damage to the plane will be proportional to his insistence (or stupidity) in trying to get through. A fatal hit cannot be excluded, but it would be about the same situation as with rubber bullets used by riot police.