I know, a lupi harness worked for mine and that is humane also.
I was just offering it as something to consider if the op didn't find anything else effective.
As far as I am aware, a prong is worn very high, right by the ears where it's most sensitive and it only takes a very tiny amount of pressure to get the dog to stop. Studies have been done on correctly fitted prongs and found no damage whatsoever.
The study did find damage from correctly used choke chains.
Dogs who wear them correctly often get excited when seeing the prong as they associate it with walks, that suggests to me that the dog doesn't find them that traumatic.
Compare that to the dogs who are headshy, who get nervous, run away or get aggressive when the choke chain or improperly used prong comes out.
While I agree that a dog could associate punishment not with pulling, but with another dog and therefore cause aggressiveness, you could get the same reaction with other devices.
On a flat collar, dog sees dog, pulls, it's collar presses against it's throat with such force that quite often the dog coughs or gags.
On a flat collar, dog sees dog, pulls, owner gives 'correction', it's collar presses against it's throat with such force that quite often the dog coughs or gags plus has an uncomfortable, lifting sensation plus it's owner telling it off.
On a head halter, dog sees dog, pulls, has its nose sharply pulled down towards the floor. If head halters are kind, then how come so many dogs end up with fur loss around the eyes and kick up an almighty stink wearing it, going to great lengths to get it off.
On a body harness, like the lupi I use, dog sees dog, pulls, gets a sensation of being lifted up under the arms.
Apart from teaching 'watch me', liberal use of treats and stop/start or turn around, all methods, including humane ones are negative reinforcement.
The prong is a more severe negative reinforcement, but it is negative all the same.
I would try and avoid using one but if nothing else had worked I would give it a go.