On one of the Internet places where I hang out, we’ve been discussing this. Someone suggested that a wide moat, pirhanas optional, might serve a similar purpose. (I suggested, as a back-up in case they survive the “wet” moat, a “dry” moat filled with dermestid beetles. (which are those flesh-eating beetles that places like Skulls, Unlimited, use to prepare their specimens).
Of course, there are the usual suggestions from some of “A flamethrower will solve all your zombie-related problems.” Some people ALWAYS go for the inelegant and messy solutions.