It is amazing that some dogs are more afflicted by this problem than others. For our dogs, we will use an ointment called Fly Repel. It has a good residual effect, but still needs to be applied at least once per day. Good sanitation is required to reduce the fly numbers. Also fly traps that utilize containers with bait are beneficial to reduce the fly numbers. In addition, if the ears have infected sores, oral antibiotics may be required to get them to heal.