As a dog ages, his digestive system becomes less efficient. It becomes more difficult for the body to break down foods and absorb them. Constipation is one digestive problem that can occur in older dogs. This can often be alleviated by adding more bulk or fiber to your pet's diet. Another common problem as dogs age is increased gas, or flatulence. You can help to alleviate this problem by raising your dog's food dish, which allows him to swallow less air, exercising him, and removing human food such as table scraps from his diet. Also check the label of your dog's food because it may contain soy which can be difficult to digest.