I found a little hill on the plains, and then shaved down all the sides until they were sheer. Then I dug a trench around it, even deeper.

I took all the stone from that trench and added a raised lip around the top with the hoe, sort of like a wall.

The entire structure is just the regular ground deformed and reshaped. It's completely impervious to damage. Basically it looks like a little castle from faraway.

I don't even get bothered by deathsquitoes. They seem to bump into the wall.