So here's a thing; zombies currently break down wooden doors and nothing else. In one of the mods used in Blood N Bones, during the zombie invasion, they can apparently break through almost anything to get to you! Dirt, stone, whatever.
Is there a mod that provides middle ground? So one zombie can batter on your door or glass or whatever until the cows come home. But get a few zombies nearby (they don't have to be in the adjacent square, it just detects a a number near to one trying to break in) and they have a chance. So much like in zombie movies, you'll see one at a glass window and you're OK, but facing a swarm you'd better find somewhere more secure!
I love the zombies in Minecraft; I want them to be a threat, but without the ridiculousness of the tearing through solid ground to get to you...! I think all this apocalypse talk in the Jampacked section has got my brain awhirl