Apply vaseline liberally to the legs of all chickens... right up to where the feathers start... treat again in a week and then they should all be free of leg mites....warning... wear old clothing.... I hold my hens and massage into their feet and legs... I have a few tee shirts that are now permanently vaseline stained!
There is a new method to try that is very cheap and seems to work according to Beekissed, a long-time BYC member. It is castor oil applied to the legs. Castor oil is very cheap too, and you can get it at Walmart or drug stores. You don't have to keep applying it that often either.