We use Frontline Plus with excellent results. No flea or tick problems and I prefer it over many others because fleas do not have to bite your dog to get the stuff that kills them. The stuff you buy at the supermarket and pet stores doesn't work very well, especially here in the south where fleas can be very difficult to control. You can get Frontline Plus at a discount price through
Revival Animal Health.
Purina One is generally not considered to be a high quality dog food. This may or may not be the cause of your dog's loose bowels. Is this a problem that has surfaced recently, or has he had diarreah for awhile? Has there been any changes in diet or environment?