I've Got three dogs that go in and out of the house daily and Yes I do know what to use but you can't get it over the counter. It's called Trifexis. You'll have to get the medicine from the Veterinarian. It's a once a month pill. It starts killing fleas in 30 minutes, it also prevents Heartworm disease and intestinal worms. <img src="http://www.lawnmowerforum.com/attachments/front-porch/21687-fleas-dog-boys2-006-jpg"/>