[quote=scaredycat]we need a second inner boundary too. and crowbars. we plan to bash the zombies’ heads in with crowbars.[/quote]
You’re talking defense in depth, now. Walls are a bit much. Barbed wire/concertina wire is excellent for this sort of thing, especially if you string it in conjunction with trip flares and booby traps.
Crowbars are also low tech, plus you have to get close enough to use them. That means getting within reach of the zombies (see Arraya’s warning above about the superhuman strength).
I’d rather sit back and pick ’em off the wire, personally. Sand bag yourself in, maintain good fields of fire, maybe pick up a good light (M249) or heavy (M2) machine gun, or five, and throw a good “rock and roll dance party” every night.