I use Sentinal prescribed by the vet on both of mine. It's for fleas, ticks and heartworm. Taco's been on it since he was 3 months and Buster's been on it for 8 years. I've never seen a flea on either one of them. They're the flavored chewables and they both eat 'em right up like a treat. I guess they're kind of expensive. About $32 a month for both pills. Mostly because of Buster because it goes by weight and he's 80 lbs. But, it's worth it to know that they're protected.