We had a Lab with awful skin problems, we got her tested, she was allergic to all sorts. The main one was grass and tree pollens. Her hair would fall out, she had very red skin and always had sore and itchy feet.
She was never walked on grass at all.
Like Jane says some dogs respond well to a holistic diet..... we read about a holistic dog food, we put Meg on it, and a few months later her skin had almost returned to normal, and we could even walk her on grass.
This was after being on steroid creams and tablets for a long time.
I'm not saying this will help your boy, but anything is worth a try. We use Burns and Nature Diet.