Hello-
It's not an uncommon habit, and the medical term is copraphagy. Why he stopped likely just had to do with a mixture of maturing and having tasted what to him was a not so tasty sampling of it, and the best treatment available is to add a supplement called For-Bid to his feedings to once again let him have an unpleasant surprise next time he tastes it. What this does it puts a bitter taste to the feces and when your dog attempts to eat it, learns rather quickly this is not something he wants to start eating (again). Usually in just a few attempts, they stop trying, and the For-Bid generally can be stopped once the habit is broken again.
For-Bid can be bought at many online pet catalogs, pet supply stores, and pet stores, as well as some vet offices. Here's a link to one such place that sells it and just to show you what it looks like:
http://www.petmarket.com/forbid-stop-stool-eating-12pkg-p-1678.html
Best of luck, and let me know if I can help further.
Christine
Certified Veterinary Technician
Licensed veterinary technician (B.S. Mercy College), 10 yrs in animal medicine and training