I’ve always thought paintballs loaded with ammonia would be good deterrents. Lower the muzzle velocity to say 150 fps so they would still sting like heck, and the fumes would choke the targets out. Let alone if you got any in your eyes. Cleanup is easy with a mild vinegar wash, and the residual nitrogen is good for the soil.
There is already something similar out. Paintballs loaded with dry O/C powder or liquid O/C-C/S mix. I have seen them used up close and personal to great effect. They actually go out at twice the FPS than normal paintballs so they sting like a B*tch too. They also have a UV dye marker in them so there is no doubt who was or was not involved in an incident.
CC