A guy is working from my property to repair a neighbour's roof. How can I protect myself against damage?

There's a damaged roof overlooking a neighbour's house owned by the guy who is putting up scaffolding on my property to repair it.

How can I protect myself against any damage caused by the scaffolding and the worker? And how can I be sure that, if he was to have an accident, that I would not be liable for damages?

View this post on my blog: http://madeinhome.info/a-guy-is-working-from-my-property-to-repair-a-neighbours-roof-how-can-i-protect-myself-against-damage