Maybe they could set up cctv around the stones. They'd have evidence for any wanton vandalism and be able to make prosecutions, as long as you can catch the buggers of course.

I still don't think the mindless acts of a few dicks should close access for the generally well behaved masses. The amount of 'ritual' crap I see, and 'offerings' left at numerous sites beggars belief. It isn't just Stonehenge that's under 'attack'. with the exception of the graffiti, I don't even think it's even wanton damage, just an ill advised and poorly thought through act.

Maybe EH or whomever is responsible for these places could draw up and locate at each site a plaque stating an expected code of conduct when visiting these special places.