My dog's fleas wont go away?

We've had my dog for three years, and he is always getting fleas. My family has tried everything. Flea collars, flea treatments, flea & tick shampoo, bathing him often. But they wont stay away for more than a few days. and recently they have gotten so bad he has open sores where he has started bleeding from biting. is there anything that can actually get rid of them?