dogs and poop

Question
I have a 2 year old male black lab/bull terrier mix.  He is a real good dog and seems very healthy.  We feed him twice a day, morning and evening but he is insistent on eating his own poop.  I there something wrong or do dogs just do this.

Answer
Most of the time, cophragia (stool eating) is a puppy problem that is eventually grown out of, but many things can contribute to the problem maintaining through to adulthood. One theory is that there is something nutritionally lacking in the diet that the dog is trying to get by re-digesting his waste again. Another is if the dog is raised in an environment where he is made to live in his own waste (such as a puppymill environment, or a neglectful owner), the dog may develop this habit in an attempt to keep his area clean. Some dogs do it out of boredom, if they are left outside alone.

What do you feed him?
Is he an indoor or outdoor dog?
Have you done anything so far to try and stop the problem?