Will Falconer, DVM Moderator
Robin, I'd also look at diet and vaccines, as it sounds like something is weakening your dogs, making them more susceptible to a pest most don't deal with.
For example: change kibble to raw, and you're likely to see a huge uptick in resistance and coat health. Here's a good page to learn more.
If you're being prodded to revaccinate dogs who've already had vaccines, odds are high they are already immune and more vaccines not only don't add to that immunity but can actually make your dogs sick. More risk than benefit. I've got a series of articles on this, your #1 most important decision.