Answering the question which I had asked myself before: I'd cut and stab the dogs throat until it stops moving. This is the only part in your reach in the situation described which is vital and not covered by ribs or skull.
Recently I walked in a park. 5 dogs (2 big, 3 medium sized) ran towards me. No owners in side, no lashes... I stopped. After the dogs were 30yds close, I pulled my 9mm and checked out where I could fire a safe warning-shot into. There was plain lawn beside my path. The dogs ran closer. As they were 5yds before me I fired.
I didn't even fire in the direction of the dogs, but right into the lawn at my side. The dogs virtually truned 180° in a split second and dashed away.
Take care.