Ring worm is a fungus. Athletes foot cream works but the best by far is Monistat that is used for women's yeast problems.. make sure that you treat any and all spots on the dog because it is real contagious.
Also if your dog houses, coops, flooring or kennel panels are wood, get some iodine based teat dip that dairy farmers use for disinfecting udders and paint all the wooden structures in your kennel. The dogs get itchy and rub on the wood and then the fungus spores are transfered to the wood and dogs get reinfected
Hope this helps
Swinging O Beagles