I kind with you there Paulus.
Making sites less accessible does protect them. It's a tough one though as we should allow and even encourage people to experience these wonderful stones. On the other hand, vunerable sites must be protected. I think Daveys suggestion of replanting heather is a good one although research has shown that a covering of heather can actually speed up the erosion process (I learned that from Graemes new book). Bracken is a right pain in the arse to get through and may be less detrimental to the stones than heather. Gorse is premier league deterent, only a seriously determined nutter would drag a can of paint through a gorse thicket.

Ultimately though, I guess it's a matter of education and instilling a sort of neighbourhood watch ethic within the users of the moors.