What kind of flea and heartworm prevention is he on? I'm in Southern Ontario (Canada) and I give my shelties selamectin (brand name Revolution) and it's a liquid that you put onto their skin at the base of their neck once a month. It's really good for protecting against fleas and heartworm, but not so much against ticks, so if you're in an area with a lot of ticks, you'll need to supplement with something else. (We use Nexgard for the ticks). It's worth asking your vet about the Revolution, especially if your dog is difficult about taking pills. I think Advantage Plus is also a liquid that you apply once a month and is better for ticks, but it's not one I'm overly familiar with and have been out of the field for a few years. But definitely ask your vet about a topical medication like Revolution, they should be able to recommend something for you.