You could put a few boxes or vending machines in the guard towers, so humans can block the ladder. Also you could put a breakable bridge between the 2 towers.
the fences are electric im trying to make it as even as possible but its hard to do that cause when you make a map your always think'n about getting away from zombies instead of being 1. i gotta get a server so i can play zm on it so i can find out what to do with some things so i guess i wont kno thill then : /