I know it's bad of me, but when you destroyed your house I couldn't help thinking how hilarious it would be if the rollback hadn't worked.
But seriously, it sounds like you're doing good stuff, and it's looking good. Do guests have permission to access chests/place minecarts and boats (the latter at least I think they should)? And do they have a means of gathering tools like swords and food?
Oh, and is it possible to turn off friendly fire just for certain groups? For example, I wouldn't want someone killing me and nicking my highly valueless inventory
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I'm also thinking of the possibility of a griefer killing all the animals in a farm. Not that I expect we'd invite people like that, but, well... is there ought that can be done about it?
Oh, and does your inspect block thing say who detonated creepers?
I'm aware this is starting to look paranoid; mostly I'm just wondering. I'm aware that we can't cover every possibility and it's a risk I think we're all happy to take.