I like the idea of desecrating a site by placing a stone wall through it but then not having the bottle to completely destroy it for fear of what may happen. I reckon that good old christian superstition has probably saved many a site from total destruction.
I take your point about the siting of rock art too. It makes me wonder if those large carved boulders could have also been territorial markers. Which leads onto the question of prehistoric boundaries. If we suppose that monuments (and large, visible rocks with carvings upon them) were sited in the 'liminal zone' i.e. the edges of a territory, and just suppose that the monuments were places seen as neutral ground, then the prehistoric boundary could quite easily bisect the monument as it could be seen as belonging to the peoples of either boundary. Could the modern walls that have been erected upon these monuments then be seen as a sort of fossilisation of a prehistoric boundary? and therefore continuity of use?
or maybe I'm just a daft get with a little too much time on my hands?