[j_philipp]

In open areas yes, though please don't :) it's a very open world relying on each of us to do good. (Destructions of established blocks will leave dust that is traced back to you, and allows the undoing of the removal.) You can make a new area though where you can set the permission to you/ you and your friends only, meaning someone won't be able to remove a block there. Created areas with such permissions have another benefit: even your friends can enjoy them as explorers, trying to solve quest puzzles and such. I've made one such area here, for instance, an adventure game: http://manyland.com/newpolis

[Excavator]

Well, that was a silly ending but always fun to team up with some random anon.

Have you looked into implementing some form of AI/bot API or the like? With the major workload being done on the creator/owner side.

[redler]

That's a clever approach (dust trail). How do you reconcile the undoing of the removal with any new structures built in that same location?

[j_philipp]

If something is placed over it, you can then remove the new block to show the old dust again, so you can undo even then. Dust only shows if the old block is considered established, which looks at ranking and time it was placed. The undo system kind of evolved over time...