There are a number of supplements and taste detracting substances you can try; in my experience, these are marginally successful. The only trick I have used successfully is putting hot sauce on the things a dog is eating/chewing so that he learns that these items are unpleasant.
Check with your veterinarian first before trying hot sauce just to be sure there are no problems in your specific case.
INTRODUCE A NEGATIVE
First, put some hot sauce on a rag or paper towel and let your dog sniff it. Allow him to lick it if he wants to (although many dogs won't try it, but back away). Reward him with praise for turning away without tasting. If he tastes it, he is likely to drool, shake his head, maybe paw at his face. Don't allow him any water for about 20 minutes, so he can't relieve the bad taste right away. Now he should associate the smell with something he doesn't like.
TEST ON THE ITEM YOU WANT HIM TO AVOID
Next, put the hot sauce on whatever it is that you don't want the dog to eat, in your case, poop and introduce it to your dog. Let him sniff. If he turns/backs away or avoids it, reward him with praise. If he eats it, allow him to drool, etc, and don't give water for about 20 minutes.
PROOFING
Later in the day or the next day, put the hot sauce on the material/poop and introduce it to your dog. At this point, he should turn away. Praise profusely!
Keep putting hot sauce on any poop in his area for about a week, until he gets the idea that if he eats poop, it might be pretty unpleasant. Once you see him turn away from poop even though you have not put any hot sauce on it, praise profusely!!! Offer your dog a treat or highly prized toy.
Occasionally go back to the above steps if you think your dog is regressing.