I find I can do a better job of protecting Frosty if she's with me. A couple of times she's run away from me and I haven't been able to help, cos I can't run that fast. So I keep her on lead.
If the other dog was staying at a safe distance out of reach - there is no way I'd let Frosty go "get into it" no matter what she said about it. I'd yell at the other dog, and I have used the end of the lead as a weapon - it's nearly 2m long so that gives me 1.5 to swing at the other dogs. It worked quite well when we were harrassed by two kelpies the other day. These dogs were trying to get Frosty to chase them and they weren't being very polite about it. Neither was Frosty.
I've also been known to kick a dog to get it to clear off. But usually standing up straight and tall and ROARING at it - works. And attracts help from any people in the vicinity.