We use Sentry pills for the outside dogs. They have to have heartworm protection and the flea meds are in the pill too. All the cats outside, all five of them (we have acres of lawn and yard) get Revolution once a month and a pill. We get a lot of stray cats here. I lure them with food and get them in the carrier and they go to the vets to get fixed and then released. If the cat runs loose around my property it's going to be fixed. The world does not need another litter of helpless kittens.