Say No to this Face?

The dogs, i.e. the rottweilers, here get a chance to run the premises most mornings. My backdoor seems to be a regular stop, albeit brief, on their check of the perimeter. This is not a photograph of me losing my hand; I'm just trying to stay on the good side of, in this case, the mid-sized one. They can't resist a good ear rub, but I'm wondering what the reaction will be the day I don't feel like patting.