i've been plagued with darn chicken snakes this year, i've had 6 this year. best i can figure, they come in during the day, while i have the chickens out, with the door propped open for the girls to return to lay. either that, or they are climbing some nearby trees and coming through the chicken wire roof of a 10'x16' yard, and going into the hen house. there is 37'' high steel roofing panels on three sides, and the wire section of the yard has 1/2x1/2'' hardware cloth on it, 36'' high with 2 layers of chicken wire above. the snakes were not a huge problem, until the biddies showed up. i ain't tolerating stupid snakes eating my peepers. i spent about 2 hours building, and installing a 36'' half door, with the plan of opening the big door and letting the girls fly in and out over it. my chickens are too stupid to do this though, so i'm back to leaving an open door during the day.