meta, have you tried the canned air sensor devices that are usually sold for keeping cats off counters? My dog's just as scared of a blast of air as my cats, so it works with him, too, and the pets don't come to associate it with me like if I had a squirt bottle in my hand. And it's just air.
Edited to add: I am another owner of an on-leash-horror dog. I keep trying the positive approach of giving treats before he goes ballistic, but really all it takes is for my dog to get the slightest hint there's another dog or person in any visible direction, and he's already over the threshold and in full Tazmanian Devil mode. I have surgery coming up and the thing that has me most concerned is trying to walk him in the weeks post-op when I'm not supposed to do anything like vacuum or mop -- in other words, no arm pulling by the dog on the leash either.
Okay, just ordered a GL - it's about $11 on amazon w/prime, hard to argue with that even if it's a total bust.