Stool eating (COPROPHAGIA) is not "normal" for dogs. Though I guess it could be a behavioral problem, I doubt it. Corophagia is usually indicative of either a medical or nutritional problem.
Nutrients are released into the stool, so when a dog eats his own poop, he usually either has a deficient diet (not getting enough nutrients out of his food), or has a medical problem which does not allow for him to fully metabolize his food (possible digestive enzyme deficiency, aka pancreas problems, etc), or possibly some other medical issue.
Most of the time, changing to a more nutritious food is enough to correct the problem. So, if you are feeding a commercial "pet food", I'd consider switching to a more "natural" type dog food (one without chemical preservatives, etc). Also, looking for dog kibbles that are "baked" as opposed to "extruded", also helps, as extruded dog food is made at extremely high temperatures (which destroys a lot of the nutrients). If you can, feeding a high premium "natural" dog food, and then supplementing about 25% of the total food with "fresh meat" (lightly cooked, if you are scared to feed RAW, or do not know about RAW feeding) would also help to ensure a higher nutrient load. Eaglepack and Solid Gold, are 2 dog kibbles which allow for the 25% more "fresh meat" addition, without disturbing any calcium/phosphorous balance to the diet. Call the manufacturers, to find out which lines in their brands, allow for the meat addition.
I'd also suggest you try adding a "digestive enzyme" to the dog's food. Digestive enzymes will help the dog metabolize the food easier (helps him get more of the nutrients out of the processed dog food). There are animal based enzymes, and plant based ones. I prefer the animal based ones, as some plant based ones contain ingredients which can cause "fermentation", and that can lead to other problems. You can find Digestive Enzymes at Whole Foods, as well as online (check for Azmira Digestive Enzymes at azmira.com, or find the Bertes Zyme from the b-naturals.com site).
And adding a "probiotic" product also helps the immune system over all. I'd look to a human grade probiotic, which you can find at health food stores. NOW brand has a relatively inexpensive one, and I am sure there are others. Look for ones without "FOS", or any other types of sugars.
I think that by making those 3 changes (new food -- with or without adding in a bit of fresh cooked meat; adding a digestive enzyme; and adding a probiotic), you should begin to see a quick end to your dog's stool eating problems. I would keep a close eye on your dog when he goes out to poop. Pick the stool up immediately after he goes, so that he can not get to it. Depending on how long this behavior has gone on, there is a chance that he has now just become accustomed to eating it. You want to make sure that you not only treat the internal issue, but you also need to correct the behavioral problem at the same time.
Here's a good article to read, which comments on "dog food" and why there are so many incidences of digestive issues, and what can be done to help your dog digest his food more efficiently:
http://b-naturals.com/Spr1999.php A lot of the article deals with how "dog foods" are just too grain heavy (a point I completely agree with). If you want to remain feeding processed dog foods, do read the labels closely. Make sure that the first 3 ingredients in the food are high quality meat proteins. If the first 3 ingredients contain grains or "by products", I'd opt not to use that food. Canned foods are also easier for the dog to digest, than kibbles. But regardless of which you use, just make sure you read the ingredient label closely. The digestive enzymes will definitely help the dog digest the grains, as well as other ingredients in the dog food, more efficiently.
Good luck!
My mom was very active in Rescue, and we had many dogs that had this type problem in the past, and the above methods worked like a charm. I also had one of my own dogs to have this issue. It too, cleared up with these changes. I have been fresh cooking for my dogs now for over 8 years, and have not ever run across this problem again (but going 100% fresh cooking takes a lot of study, so please do lots of research before attempting that, as you can create a lot of health issues if you do it improperly --ie, calcium/phosphorous imbalance, electrolyte imbalance, etc).