Heya, I use Comfortis for fleas on Oskar. Bit pricey but it's worth it! Chewable tablet and he has nooo fleas at all!!! Heartworm, he has a needle I think, and Intestinal worms, a tablet every 3 mths.
I would agree with this treatment. we learned yesterday from the vet that there really isn't any treatment that is "water resistant" - it loses its effectiveness with every wash so the tablets are the most reliable.