To prevent this from happening, I came up with the one thing that works for me. (so far)

Wait one day + night on the spot where you want to build and observe where the spawners are. With that knowledge, it's easy enough to figure out where not to build.
Using this "technique" I have never seen a spawn inside my walls. (Probably also depends on the size.)

I've read people saying workbenches prevent spawns... which is not true as far as my experience goes.