Yeah, I get the frustration when you have a dog that you need to be careful of. Like I said, my parents have a dog-aggressive dog, and dogs (of any temperament) who are uncontrolled off-lead are very annoying since then you have to deal with the dog who's being aggressive and the other dog who's just being clueless.
A lead on my dog would not have made a difference, in this case, he was already walking 18" away from me before we ran into the other dog, and when he saw how crazy that dog was, it turned into about 3" away from me. If I couldn't control my dog at all times off-lead, I wouldn't walk him off-lead (even for 5 minutes).