Surely most people (excepting swastika carving types) are quite reasonable, and many of these climbers probably know nothing about the rock art. I'm sure if they were told about it most of them actually would be interested (after all, they are Outdoors Types and probably interested in keeping the environment reasonably nice). Consequently they might at least try not to erode it even if they carry on climbing round it. Aren't people generally ok? I think you're being a bit cynical (and I am queen of cynics).

In this instance it is you who needs to 'get real'!

We are not talking about stopping complete fucking idiots damaging sites for kicks! Twat! <backspace><backspace><backspace><backspace><backspace> Sorry ...

Nothing will deter the nuts who will carve swastikas into things or dawb them with paint, but you can let the good folk out there know that there is something important on a rock that they should avoid using as footholds.