My sister has a dog that she keeps outdoors. Lately I've noticed that flies seem to be biting him a lot. His nose and ears are the places where he gets bitten the most. He can usually take care of his nose by himself by rubbing it in the dirt (Lots of animals do this in the wild to get rid of flies) but his ears remain vulnerable. They are always bleeding and scabbed from the high concentration of flies that bite. I've tried several things to get rid of them, such as apple cider vinegar and petroleum jelly but nothing seems to be working. Can anyone help me out?