You're never going to be able to protect sites from the ravages of nature though. Surely we'll end up encasing them in glass domes if that's the route we choose to follow? I do appreciate your point, but I feel that there's a very difficult line to tread between conservation and continuing use, and I'm really not sure where that line should be drawn. Should we prevent all access to monuments? What if we carry in a seed between the tread on our shoes that then grows to become a tree the roots of which undermine a stone? How do we determine what constitutes reasonable risk?