Im still young enough to run very fast so that would be my first option, but If I could not run it would be warning shots and 50 yards and kill shots at 20 yards. +1 on pepper spray too. I have seen some larger cans of the pepper gel that shoot out to 30 yards. The anarchist's cookbook and the poor mans james bond have all kinds of recipes for dealing with this exact situation. And as for how I would justify myself. . . In either case I would rather be alive and in legal trouble than just plain dead.