If the dog is a trained personal protection or police dog and it is a good specimen: You have no chance. All of this nonsense about kicking the dog at the right time is baloney. Your best chance of surviving is to stand absolutely still. If you are unarmed, and you try to fight the dog, you will lose. The dog is fast enough to bite you two or three times before you even realize where you've been bit. And by then... it's over.