Yes, Harry is mega protective of Sophie when she's in heat. Just hates other dogs if we're out. But that was when he was intact. Buster has met many intact males while Sophie is in heat, if they hump her to much he gets a bit PO but otherwise is fine.
Oh.. should add. Sophie is our 40kg mastiff/boxerX, she only EVER seems to attract dogs 5kg or smaller, meaning they used to slip through the fence, we would always supervise when they were around and lock her safely away when we left as I know even the smallest dogs can be tricky. 10 years and still no pregnancy so we must be doing something right.