Ring worm (I think) is the same thing as heat rash. Which is the same thing as Athlete's foot, jock itch, etc. It is very common in summer (hot months) for humans so I would assume it's also common for dogs. -- I had a heat rash in my arm pit this past summer (hey, it happens
) this is why I know so much about it.
My close friend who is a dermatologist suggested I use two over the counter medications to get rid of it. They worked great.
First, go buy your dog some human hair shampoo. Give it a try, it's called NIZORAL. It is sold in every pharmacy and comes packaged in a box. This should immediately help the itching.
But to get rid of the rash, you are going to need an anti-funghal cream (I assume) It takes about six weeks to rid the rash but after using the Nizoral, there should be no discomfort.
So for cream, use Lamisil. Maybe put some socks with rubberbands on your dogs feet so he doesn't eat the cream. You will have to use the cream in two doses a day. Morning and evening. Repeat for six weeks.
Good luck.