These small brown insects hide in cool, shady areas among shrubs, leaves and tress until a host (like your dog) passes by. The flea(s) then jump on your dog and are brought into your home, quickly becoming a menace. In fact, according to the American Animal Hospital Association, just one flea can multiply to 1,000 fleas in your home in just 21 days. Suddenly you and your dog are itching, scratching and picking at scabs. Even worse, fleas can bring about tapeworms and other serious diseases. Save yourself the headache and prevent infestations before they start by using a flea preventive for dogs. They come in various forms to suit you and your pet's preferences, including flea collars, spot-ons and even oral medications.