There is also a product called "Halt" that will stop a dog but not do damage.
http://halt.com/halt.html
Thank you for the suggestion, Irishgal. I was going to ask if anyone could recommend something. There are lots of positive reviews of this product on Amazon. It's basically pepper spray, not strong, but apparently enough to cause the dog to back off.
We too have had attacks while walking our dogs. Afterwards I've called animal control and the police, and they just chuckle and say they don't have the manpower or funds to look into complaints of dog attacks, not even when there are bites.