Maybe you could get the county to allow only members of a local AMA recognized club to fly. Fliers would be required to have on their person current AMA and club cards. Anyone not complying could be considered trespassing or violating local ordinance or something similar. With this in place you could call the cops on the offender and have him/her cited. I know that the cities are not looking for more laws or areas to enforce, but at least you the responsible modeler will have some backing when the situation occurs.