Griefed worlds.. to the boom

My server's been running for about a year now. There have, of course, been many struggles but for the most part I've been able to cope with them.

But one problem remains - griefed worlds. Since my server is a raiding server there's a lot of explosives etc. This means that 1000x4 block worlds get completely griefed in a matter of weeks.

Now this isn't good because who wants to play on a server with no resources left to obtain, nothing left to explore and no dungeons left to conquer.

What do you guys do about grief related problems? Is there a magic trick I haven't found out about yet? I do use a resource world which resets every two weeks, but new people are having a hard time knowing where to not build there house and where to get resources from..

A few ideas to chew on-

Plot based world
World where to build, you'll have to put down something like a claim stone which covers a certain area in which you can build. As I mentioned, my server is all about raiding, so this would kind of ruin it.

Sky world
The only world on the server that wouldn't get reset ? You'd live in the sky, get your own personalized island with stuff. You build an empire and try take over other islands by building bridges. Or how about you have to pay for bridges, the more money you feed it the bigger the bridge gets. Still a weird idea

- Da sexy chocobo