So I have a pack of 6 dogs outside my home that I feed daily and there is one older female dog that has a rash on the back that is itchy and the doggie often lays on the back and twists her spine to scratch it.
I have taken some pictures so you can see and maybe offer some advice in treatment. I have washed this dog once with a pest control veterinary soap but the rash persists.
The female is old, maybe round 8 years or so by my estimation, lacks front teeth. The yellowish patch towards the shoulder area is some sulfatiazol I applied to see if it helps.

I dont have much resources to take her to the vet.
I appreciate your input.
Thanks.