The 1% injection for cattle and swine for dogs...except collies. I've had Golden Retrievers for years. They are about 80 lbs. I use > .07 cc/ml every month. Start off with a smaller dosage. If your dog is 90 pounds start off with .03 first month, .05 next, until you get to .07 or .08.
I draw it up in a syringe and squirt it over dog food.
My vet told me the reason he is totally against this is because the Heartgard he sells is paying for his staff, saltwater tank, etc. He is an acclaimed vet that has earned many accolades with over 30 years experience.
My dogs never had worms or heartworms. Just sayin'...Most vets hate this.