I just stand still and keep a firm hold on the leashes of my dogs and remain quiet. Yes, thats happened to me loads of times and our Jess and Mist did give the others dogs more than they bargained for but they were on leashes and, generally, when the other dog realised they had bitten off more than they could chew, they'd walk off in a huff with no damage caused to either party.
I wouldn't worry about the owners of the other dogs because it's theirs that are out of control in a public place and so would be them that got into trouble if it came to it.
Our Jess and Mist were both capable of standing their ground and even winning with most other dogs so I didn't need to protect them myself...they tended to get rid of the other dog themselves....lol.
I would never have started shouting at the other dog because that would just rile our Jess and Mist up even more and that was the last thing they needed. I had to remain calm and quiet in these situations so as not to send the wrong message across to them. They were already mistrustful and aggressive with other dogs as it was, especially our Jess. I'd only have to stamp my foot at another dog and she'd go barmy wanting to shred it to bits.