Olive oil works very quickly; cleared up my dogs dry skin in less than two weeks (though I put it in food) and is relatively cheap. Three table spoons a week I think is what vets have recommended. The high fat can cause some laxative issues though. You don't likely need fish [cod] oil after that, though if you have a decent fish source….never hurts as a supplement. Especially salmon. If you're neurotic about your dog's health [ as there is some controversy surrounding Olive oil], and wanting to pull out all the stops, just go straight for the fish oil.