As a runner I have often encountered aggressive dogs running at me. Most of the time turning to face them, standing my ground, and firmly saying "Go home." has stopped them. I then slowly back away. You definitely have to read the dog. I had one dog that this did not work for. With him I had to stand still and not move. Thankfully, his owner would come out when he heard his dog bark and call him away.

This would be really scary if this happened! What should we do?

Stand tall and appear as large as possible. Show the dog you're ready to defend yourself. Generally, dogs tend to be submissive. When people typically run, jump, or scream in response to an aggressive dog, it boosts the dog's confidence, leading it to act more aggressively with each passerby. Be assertive; take a step forward and say, "No, go home!". Never go backwards; you will be submitting to the dog.

Pull your gun and put the animal down.