I have been visiting Box since the 1980s and the graffiti has not changed much, being mostly in jacks working, once under the boulder at Black Horse you leave it behind. You will find it again in the vicinity of backdoor.
The Monkton Farleigh conveyor passage is a total mess.
Browns is a tug of war between the vandals and the 'caretaker'
I suspect all the aggro comes via the M4.
Talking mines rather than caves, in other parts of the country the problem is no where near so severe, totally absent in Wales bar some silly arrows in Hendre Spar, Dinas Silica is wide open and nothing at all. North Pennines, a few arrows appear now and again in Smallcleaugh. Cornwall, never seen anything.
As the owners of Cwmystwyth, CMT could gate everything but we have no interest in this at all as its would be a solution to a problem which has never existed.
We would rather spend money on reopening lost ground and improving access rather than restricting it, a fact that is universally known, and universally appreciated.