Cloves. Soak them, make a tea, spray around the coop. Or oil of cloves. The coop smells good, too. Snakes have to be really motivated to cross a smelly line (their olfactory powers are remarkable). Tried it last year after finding, catching, taking for a long car ride and dumping, many very large rat snakes. Sometimes I would open the nesting box and see a five-foot snake draped over all the nests like a Christmas garland. One was under my broody hen, I grabbed it with my snake loop, (which was easy because it had swallowed an egg which was halfway down) and managed to get it to spit the egg out so I could put it back under the hen! Started using the clove "tea" about August and didn't see a snake since. Just bought some clove oil and I am looking forward to using it and saving some money over my dry clove purchases. Remember that moth balls are a toxic, nasty confection, not good for you or your chickens! And sulfur just stinks. I have also heard that a big ol' turkey will keep the snakes away as well AND eat the mice! Hey, any excuse to have a big ol' turkey is fine with me!