I have to agree with most of what was said before. I guess it's a primal urge that is deeply routed in some (if not all?) of us, but at least for me it's something to stay strictly to fantasy, mainly because I guess it wouldn't work out the way in reality that one might imagine.

just think about it, it's one thing to teach your dog to stay at your side when called, but a wholly different cup of tea to get him to hop on your girlfriend's back. I don't even want to think about how such a dog would behave in public