How can I cure my dogs ear?

I have a golden retriever who is 9yrs old. He gets mites in his ears but we clean them out. His one ear is BIG, swelled up. My mom is putting zinc on it and she is cleaning his ear out with doggie ear stuff. This happens often with his ear and i know it bothers him, so i wanna take care of it. We went to the vet last summer and the put some kind of tube in his ear to drain it but that did work cuz his ear still swells up. What is something we can do that will permanently take care of his ear???