Stop trying to poison your dog. Like you said he isn't stupid. My beautiful black and red long haired straight from German stock German Shepard is seven years old and she is outside a lot and has been negative for heartworm every year. The only reason I keep allowing the blood test she hates so much is so they'll give me the heartworm chewable I sometimes give her in the summer if there's lots of mosquitos. She eats them with no issues, there's no tick and flea poison in them. Have you tried something topical like Advantix for the fleas and other biting insects?