I guarantee that if you kick any dog hard in the face then it will run away crying. I know this because, unfortunately, I've had to do it to defend myself. I was about 16 and riding home on my bike. A large Rottweiler ran out in front of me and I fell off as I swerved to avoid it. It initially walked off, but when I stood up it turned and ran at me with its teeth showing and growling. As it got in front of me I kicked it in the face as hard as I could. I don't know why or how to be honest - I think it was because I was still worked up from falling off my bike. The dog initially stopped, turned, staggered for a few seconds, then composed itself and ran off. There was blood on my shoe and the floor. I'm sure that if I'd have moved towards it or made a sound it would have gone for me again and I'm not sure what I'd have done then. Anything bigger though and maybe my kick would have had less of an effect. This dog was, I'd say, about half a meter tall and maybe 40kg. I'm not proud of that and if it happened again now I'd probably be bitten to death as I wouldn't want to hurt it
My Mum also used to have a huge Doberman cross (though I can't remember what with!) and when it stood up on its back legs it was taller than my Mum is - 5'4". When she got in from work he used to run up to her, pin her against the door by putting its paws on her shoulders and lick her face! It used to play with her and would leave teeth marks in her arm from where it play bit her, but never once hurt her or drew blood, even by mistake. One winter she was walking him in the local park and throwing snowballs for it to catch. They started playing and as normal it got hold of my Mums arm and started pulling. This time though it really grabbed her hard and wouldn't let go when she told it to as it normally did. It started to hurt her, but rather than freaking out, she kept a level head and reached back and grabbed hold of its balls and squeezed! Lets just say it never grabbed hold of her arm again! This is an entirely different situation to a dog attacking and she knew the dog, but it still let go, which could suggest another dog might too, especially if you kicked it there rather than just grab.
Even after them experiences I think that if a large dog was determined to get you or got you off guard then there would be little you could do. Though if you were a large, fit guy then you would probably be able to fight it off eventually, but you would certainly be seriously injured.