often it's just something puppies do and they get over it. you can try feeding him some pineapple, which is supposed to make the poop taste less appealing. it might not work, but it's harmless at the very least.
read this - if it makes you feel better:
http://www.greatdanelady.com/articles/stool_eating.htm
You can also buy some pills, i use Deter by 8-1. Coprophagia Treatment pills. So far so good with Oreo (he's a poopy eater or was)..
best wishes!