I foster, many of them mill dogs, so I have lots of experience with roundworms. As LoveisGolden stated, Interceptor treats heartworm as well as hookworms. whipworms and roundworms and I keep my three family dogs on Interceptor year round. I always treat my fosters, even when the vet has initially found them negative, with Panacur...I do one round when they first come here and another round two weeks later, I wait a month and have the stool sample done again. Worms can be picked up anywhere so even if I didn't foster, I'd keep my dogs on Interceptor year round.
Jan, Seamus, Gracie & Phoebe