Nivea cream. My horse is always getting into fights and comes back with scratches or patches with no hair. I tried pretty much everything and the only thing that has worked for me is Nivea.
I clip the entire area, give it a good scrub with stanhexidine, and they were really stubborn so alternated with fisks, an antifungal called blue coat, dermal gel and colidial silver in liquid form
My vet suggested that I trim the hair as much as possible and alternate cleaning the area with an antifungal/antibacterial shampoo and a scrub like chlorahexadine. Then cover the area in a product like Furazone wrap with gauze and vet wrap to keep out dirt and bacteria.
I usually clip the hair off of the area as best as I can (not clipping off the scabs), scrub the area really good with a betadine scrub and then with an anti fungal soap. Then treat with either mTG or some sort of antifungal treatment.
I like to use an ointment called SWAT and MTG to help the hair grow back.
In terms of prevention, polos or back brush boots may cover the area he is scratching himself (assuming this injuries are happening while you ride).
I use an ointment called Fiskes on my horses. It usually works pretty well.