this simple design is a wooden pillar with a 3x3 platform on top with a hole in the middle and a wooden ladder on the piller .
if you stand on the top of the ladder the zombies will try to climb it , but because you are standing in their way they cant continue climbing up , they cant hit you because you are standing on top of them and they will rarely even attack the pillar .
when i tried it at day 7 horde the zombies were just running around the pillar and didnt even bother with attacking me