Kicking a dog can work, but you'd be suprised how little agility large dogs have. They are also not as stable as you think they are. Most dogs when attacking will instictively leap off their front feet. This makes them even easier to take down. Remember to sweep them to one side or the other.
If they stay on all fours, they will be more stable and harder to take down, but unable to effectively bite at you. Arms are the easiest target and if they are above the dog's head, the dog must jump at them. When he does, you take him down.
I'd say from your description, 1 more rep, that protecting your dog from another dog would be a more difficult proposition. When an attacking dog is coming after you, he is easier to deal with than trying to keep your dog out of harm's way.
I would personally stay away from kicking a dog. Best case scenario is you land a kick and still have to deal with an angry dog. You might be able to chase him off with that, but then again maybe not. Worst case scenario is he clamps onto your ankle which will make it nearly impossible to deal with. All in all - risky.