I would give switching his food a shot. I used to feed Ethel Nutro when she was a pup. Turns out she has a horrible allergy to grains (which presented itself as chronic ear infections). I feed Taste of the Wild now, and I actually feed her a lot less than I used to with Nutro. Less poop too.
Also try treating your yard, house and rub down the dog with diatomaceous earth. It did wonders on the flea problem I recently had. And I've been putting it in the dogs' food too, as it seems to have various health benefits, one of them being a natural dewormer. I've actually been taking it myself, and it's done wonders for my bad knee and achy joints.