1.Spike: prevent people from jumping up and down to slash you while you stand at the door.
2.Little Roof: prevent archer from a simple arrows jump to get up.
3.Back-wall: Support the tower from 1 hit bomb. 2 layers of stone or castle background may be needed.
4.Stone: It can slow down some digger and also support the spike.
Resources: 100 woods; and 114 stones.