Ooops, I misread (not hands and knees). I still would go down on a knee.
If the dog really wants you down, he can get you there very quickly. In fact the very fact that the dog has approached but still kept distance indicates that you are at a psychological advantage in the encounter.
If you stay cool, you are in control with dogs.
Phooey! I hate typos. I would NOT go down onto my knee.