We had raccoons raiding our fish pond & killing fish & tearing up plants until my DH installed a low current electric wire used for fencing in animals. It's about 10 inches off the ground making it difficult for anything to step over or go under without getting a good sting. It's on a timer & turns on after dark & off just before dawn. (No more problem.) I don't know if this would be feasible for you to surround your chicken pen.