I've only been in the situation once or twice and the owners have always been there. I usually walk all 3 dogs (all over 50 lbs) by myself. So when it has happened, I think the dog/s coming after us have felt a little outnumbered.

Usually a guick stern "GO HOME!" keeps them away.

If I do see a loose dog, I usually turn the other way or go down another street. (Unless of course, I'm by myself, then I try catching them. )