Griefers want to do the most damage in the least amount of time. Therefore make tactics that are often used to grief more time consuming. Here are some suggestions.
Vaults:
In the current situation, locked chests are used to grief (by placing them at annoying locations). If they are more expensive, (e.g. 8 iron), this tactic will be more difficult.
Granite:
What if there are stronger types of stone hundreds of nodes below the surface. These blocks, and all derived materials can only be mined with a mese pickaxe. This will require any would-be griefer to spend at least 1 hour mining (and actually playing the game) before he can destroy our precious buildings.
Note: This should probably be done in code.
Bucket of Lava:
IMHO carrying lava in a bucket is strange. It is also a good griefing weapon. Therefore remove it. We can always add an expensive type of bucket that will allow the carrying of lava.