There is no way at all to prevent an attack without arming the plane with a way to deter the missle. You cannot lock down a 5 mile radius around all airports.
Better enjoy your spotting while you can. After the next attack happens it'll be all over. My gut feeling is, someone will attempt such an attack sometime as they have vowed to bring the battle from the desert to our land. But I doubt they will try it from such an obvious area as a spotting area.
Authorities will still try to drive out all spotters even though spotters can be an extra set of eyes - valuable.
Bruce Leibowitz - Jackson, MS (KJAN) - Canon 50D/100-400L IS lens