Teddy had it last summer. He has very light feathering, so I trimmed all of that off. I did not, however, clip him, although some people suggested it. I used a betadine shampoo every time I saw him (3-4 times per week). At first, I had to rub mud and scabs off, and that was traumatic (more so for me than for him, I think).
My process for treatment: I got his fetlocks all wet and rubbed off all of the dirt I could, then applied the betadine shampoo and rubbed it in really well, then let that soak 10-15 minutes. Then I rinsed it off, making sure his fetlocks were completely clean and scab free, and let him graze. Then I dried it off really thoroughly and used a product called mud guard, which is a powder that supposedly keeps mud from sticking (since I figured it was the dirty mud that had caused the problem in the first place). After a few weeks of that, when it started to clear up, I started using a less harsh shampoo called "E3 Elite Grooming Products Antibacterial/Antifungal Shampoo for Pets" whenever I saw him.
I still use this on him maybe once a week now, if he's muddy, to try to stop it before it starts again. So far it hasn't flared up this year.
Oh, and also when he first got it I put him in a dry paddock for a couple of weeks. They have a pond and a little creek in their pasture, and he kept getting himself muddy even when it wasn't raining.
Chase had it BAD when I got him. None of the over the counter topical sprays helped, at all. Medicated wash helped some, but it was still coming back.
What finally did it for him, after addressing it with my vet:
1) Wash legs in Chlorhexidine solution (buy at any pharmacy for a few dollars, hibiclens is the brand I used) Rinse thoroughly.
2) Wash legs again, this time in zinc dandruff shampoo. Lather and let sit for 10 mins, then rinse thoroughly.
3) Towel dry legs as well as possible, and apply heel cream. My vet prescribed a antibiotic/anti-inflammatory cream. My vet suggests wrapping the legs with the cream, I chose not to for logistical reasons and the cream was still effective.
I did pick off as many scabs as possible while washing... the cleaners/cream need to get to the skin underneath.
I applied the cream daily, and repeated the washing process each weekend for a few weeks. I think I did maybe 3 washes total, but just kept up with the cream and pulling scabs in between. And it cleared completely.
Now, if I notice him getting even a little patch of scabs I wash it right away and apply the cream, and it usually disappears before it really starts.