Drinking, smoking and littering mainly. Smashed glass, vomit, glow-sticks etc...
Lots of reports of this on the increase this last summer. We got the site taken off Google Maps and DCA are chatting to the owner about installing some private land signs at the top gate and car park. It won't affect caver access, but just might keep the odd unwelcome visitor away. Myself and another instructor once accosted 2 chaps walking down with geology hammers, ready to collect some samples. They were informed that they were on private land and not public land and they soon left.
Any gates or locks appearing here would not go down well with the caving community and would be a hinderance with the farmer. I'd expect pitchforks would be sharpened at the merest murmur of locks on Giant's.
If we wish to resist the need to secure sites more often though, we should consider the amount of info that we put out in the public domain that can be found very easily.
I echo what I said before, 'we' should not feel that we have to stop making films, pictures and publications for public consumption, but should perhaps consider if not naming the site would take anything away from your work and the possible consequence of greater public exposure if you did.
Not seen the sun for months. Now evolving to see in the dark.