Quit feeding them Ole Roy from Walmart. That is the most worthless, fart inducing dogshitfood in the world.
Find a food with a little corn and wheat fillers as you can. Nutro makes several excellent types of food with excellent nutrition and very little fillers. Fillers cause your dogs shit to be larger and stink more. The better the food, the better and more complete the digestion, hence the smaller the doggy mines in the backyard too. Their coat and energy will improve almost overnight.
Cheap dogfood with a high amount of fillers (corn especially) is bad for the overall health of your pet. Most dogs have a mild allergy to corn products which causes their skin to be dry and itchy. In addition to dandruff, they will scratch a great deal and their coat will appear dull. Not only that, your pet has to eat much more of it to get the RDA of vitamins etc... This is one of the reasons that dogs get overweight. Overweight dogs, especially large breeds are prone to hip displasia for precisely this reason.
Bottom line, get good food.