Slightly away from the original topic, but my brother (the vet) recommends sprinkling their food with a bit of plain Adolph's meat tenderizer. The enzymes will apparently result in greater digestive breakdown and piles will be smaller and more compact.
And for those of you spending a fortune on monthly heartworm meds, look into purchasing liquid Ivermectin from a cattle/farm coop. About $50 for a liter. Same ingredient in HeartGuard. Only takes a few drops once a month orally and is the same protection. Can't OD the dogs on it (well a gallon could I suppose), it has an indefinite shelf life. A liter will treat an average size dog for about 213 years. But you didn't hear this from me.
If you don't believe me, check here for Heartguard active ingredients:
http://heartgard.us.merial.com/pdf/Dog_information.pdf