I doubt it but would like to be proved wrong. Hard enough to get plod out for serious crime.

I suggest that you remove his 'implement' (the stone) and leave a note (with directions to the local hospital maybe). Just let them know that others have an interest here. He or she might go away.

Otherwise, camp out there for a few days and catch the bastard in the act. Just make sure they haven't got a boulder in their hand when you accost them!