You've already got your answer, but just to add onto it, terraforming to the degree you were initially asking for is a pretty bad idea. That much terraforming causes stress on the game and will eat up resources more than it initially did.

Easiest way to disable monster spawn points is by using the workbench method. Enemies can't spawn within certain distances from specific structures. Anywhere within the building radius of a workbench can't have enemies spawn, so people will cover their bases completely with the workbench radius so enemies will spawn outside of your base, and you can make them spawn really far away if you want. You can even somewhat bury the workbenches underground (not completely) to protect them from damage and keep the range even farther.