/set gamemode 0

You mean cover only the top layer so that everytime you run by it makes the nearby cave noise? You got it boss!

/gamerule mobGriefing false

Or you can make it a little pond.

FTB Chunks user: you have no power here.

I like to keep one valley not patched so it looks like place where many battles took place

I myself like using a mod so that it automatically repairs itself

Or embrace the hole and make it a perimeter

But leaving it alone adds environmental story telling for future explorers.

Fine, but since there isn’t enough dirt to fill it in I’m going to make a bunch of floating trees and fill it with wood :)