I personally like to put Vaseline on the legs. It is the most natural way, a little messy though. You can dip the legs in one part of Kerosene mixed with two parts of linseed oil (not motor oil!!!), both available at Loewes or Dixieline or so. Make sure to paint the roosts as well to prevent re-infection.
If your chickens are not laying, some people use Ivermectin 1/4 cc for Standard size chickens, 5-7 drops for Bantams. Good luck.