Just be sure that your anti-spawn blankets the whole thing if you don't want any plains enemy to pop up. My home is like this, but I let the plains enemy spawn to keep the riffraff out... they are most excellent at farming boar, deer, necks, grey dwarves, skeletons, blobs, trolls... anything that comes along is murdered every night. Its glorious. If you need loot beyond this, smack a rock with your fists or something to make noise :)