sorry running -dog but I can just imagine Gus and the exploding poop bag
Seriously, it must have been ghastly and so frustrating for you, and um somewhat messy!
Dogster has made a very good point, take your treats and clicker on your walks. I do this all the time, especially since the incident when Ra Kismet and I were attacked by another dog and he's been over reacting. He's almost 'there' now, looks for his treats rather than over reacting, and that's in just around two months. If you really cannot get to click, then treat, treat,treat. I have the clicker in my right hand, same hand I hold the lead, so I have a free hand to treat. I use the cue 'look at me' and click./treat like crazy. Along with, now he's so much calmer, chill little buddy I've got your back
LOL Ra Kismet is still a little bit like Gus, the odd moment when he attempts to lunge (doesn't go the whole hog now though resets himself and prances along looking for his treat) then next day or later the same day, walks like a total angel, ignoring other dogs. He's always been fine with people, just a nosy parker if they're doing something interesting, like putting out the trash, opening/closing their front doors etc., but never lunges.
Good luck! Gus will one day surprise you and become 'Angel Dog" never lunging, bursting poop bags or anything untoward.
And it's not your training, some dogs just take a little more time than others to catch on too good manners
LOL love the reference to the nursery rhyme, good one, something all dog lovers/trainers should remember!