Take the dog attack like a trooper, apparently nothing will stop a dog short of a gun.
Get two cans of spray and practice your shot so you don't "miss" the dog when you really need to hit him. Squirt yourself too, don't let your first experience with pepper/nerve spray be when you need to have situational awareness. Yea, it will sting for a while but it will give you an idea of it's effects before you squirt yourself in the eye when trying to outrun a dog.
It is better to have spray and not need it, than to need it and not have it. Same applies to firearms for those who ride armed (the most effective means of averting a dog/bad guy attack).
Or, just ask your mailman what he uses, I bet he has a realistic plan.
Hope this helps,
ehenz