1. Disengage if you can.
2. If not, warning shot - if you have time. This usually spooks the dog off.
3. Dog continues to be aggressive - one shot, center of mass.
4. High-tail it out of the immediate vicinity and call police from another location. Removes you from aggressive owner, lets LEO handle the situation of the dog attack/ shot being fired. 5. Tell police the truth - cooperate, you've done nothing wrong if your state allows you to protect yourself with a firearm, carry concealed, etc. If your state does not allow you to protect yourself with a firearm, move to one that does - the crime rate will be much lower there!

By the way - take your weapon and put it away (in your car, house, etc.) before police arrive so they don't shoot the "man with the gun" ! They may want it later, but that's fine. You may need a lawyer - YMMV.