The reasons listed are sometimes the cause of this behavior. But if you feed your dog a low quality food with lots of fillers & addatives then not all of that is properly digested. Therefore some food material is still in the feces making it "tasty" to the dog. It is ussually more common for puppies to do this behavior & most grow out of it. There is products out there that you can either add to their food or sprinkle on the feces. But in order for those products to work you must make sure that you dog at least tries to eat that stool. Also by always going outside w/ him you can train him not to eat it. Keep him on a leash, when he starts to eat the stool tell him NO firmly or teach him a "leave it" command and pull him away from it. As soon as he leaves it alone praise him w/ a tasty treat. When he starts to learn that then he may just sniff the poo as long he does not eat it praise him.