Hartz Ultraguard Flea & Tick Collars for Dogs and Cats Fresh scented Kills and repels fleas and ticks for 7 months. Can be worn simultaneously with your dog's regular collar Water-resistant design won't cause loss of effectiveness if your playful pup takes a stroll in the rain Fits dogs with necks that measure up to 20 inches For use on adult dogs and puppies 12 weeks of age and older