All irrational fears aside, if zombies did start clawing at your door it would not be with any superhuman strength. If they are in fact Zombies (in the undead Romero way) we can fully expect them to be decomposing from where they stand. The easiest way to ward these guys off is by simply reinforcing your wimpy wooden door with a stainless steel one.

Affordable and impenetrable to zombies and insurance salesmen, these doors will do you plenty of favors. Might as well go for the triple point locks too, zombies hate those.