Hey folks, Thanks for the replies. That was exactly the sort of info I needed. They've gone at it a couple of time since, but still, I don't think they are connecting yet. He is not new...he's fathered two litters before, but she was the alpha dog before he showed up and she used to use that same posture (humping) to declare her status. I'm sure his attempts have confused her.
They'll figure it out, and I'm here to help when they do. And tomdonna, they are about the same size. He is a little bit taller, but no heavier. He is longer legged that she is, but only by a little bit. They are both long coats, so they should make pretty babies! Thanks again, folks.
