We are lucky in this instance, they have been offline for so long the flags in the area are yellow indicating free building for anyone, which is what we have done, all we are doing are land locking it to others to claim but they have the right to do it back so it's becoming a stalemate. Right now with our flag down to steal territory, the flag griefers are running in every hour resetting back to 6 hours and running away again. It's not harming us overall with building on the area but it's pretty petty behavior. Not sure what the devs think of this or is it actually intended to be used like this because it seems pretty abusable right now.
We were talking about a wall but the area is open and vast it's not going to stop them from getting in via climbing hook so it's waste of time and resources to do it.
Again open to other suggestions though.