Chris from Pittsburg made a very valid comment which I'd like to strongly suggest is implemented and can't really believe it isn't already:
I think Chris' suggestion is a perfect answer to all our concerns. Take arefundable bond that is held for a week say after departure. I have used this method on another site as a remote host and it generally works really well. The minute loss of money is threatened it is incredible how more careful people can be. I realise it is a bit more administration possibly but would be worth even paying a bit extra (maybe this could be optional) for us to have a little more confidence /insurance in our most valuable possession.