Loose dogs are so rare around here that passing drivers often stop, pick them up and either phone the owner -- if there's an ID tag -- or take the pooch to the vet to check on whether it's chipped.
So naturally, bike-dog encounters are rare. The only worrisome meeting I had involved a big shepherd mix that was being walked off-leash. It ran at me, the owner said, "Don't worry, he's friendly," and the dog took a half-hearted chomp at me. It missed, but I could hear his jaw snapping shut. I didn't stop for a discussion, but I think the owner saw the bite attempt. Hope it taught him something.