well, when it comes to docks, the best route is to block the front and side door, and use the bottom stairs to get in. It puts the zombies into a really thin narrow hall way prim for spray, barrels, and all other sorts of nastiness. Most ZM's don't even bother attacking there since unless you're willing spend 400+ points on explosions that might not even clear the path. Although shamblers can sometimes break it on their own.