Taedyn has problems with outside treat taking, too. It's been very slow, but now I can give her treats in certain situations when outside.
Find a quiet space, even if you have to travel to get there. You may first have to get her very familiar and comfortable with the space before she'll take treats. Being very hungry also helps
I first used my back yard / car parking area. We go through that area at minimum 4 times a day, so she's very familiar with it. At first it was difficult to get her to take treats, but after I stood quietly for about 10-15 minutes, the surroundings weren't as distracting anymore and she paid attention to me.
After she was comfortable with that, I tried moving down the driveway while giving treats. Take it slow, moving step by step (could take 5+ minutes between each step) into the more distracting areas.
Last night I discovered a small quiet alley was just perfect. It was still "outside" but with much less distractions. I was able to walk up and down the alley with her giving her treats for eye contact.
As for getting him to look in the first place, just stand still and wait for pure boredom to take over. Stand there quietly, and praise him every time he faces your direction, even if it's just turning around. Eventually he'll get so bored of the surroundings and realize that it's much more interesting to be facing your direction. Once that happens, try to engage him more, scratch him, etc. Then start looking for eye contact, and praise for even a split second look at first.
Don't try to force him to look at you, or to stay with you. Let him know he has control to walk to the end of the leash, and that it's his choice to engage you. Be the most awesome of awesomeness so he wants to be engaged with you.
If you've reinforced the attention/eye contact training indoors, he may quickly realize what you're trying to do and settle into the routine. Once Taedyn gets what the game is, she immediately sits and just stares at me.
As a note about the prong, is it fitted correctly? Leerburg has a guide.
If it's snug under the base of the skull and dead (so it won't tighten like a choke collar), it's theoretically supposed to not be an annoyance to them. If he reacts aggressively to the pop itself while fit on the dead ring, then you're right that it's not a tool for him.
Another tool to try would be the easy walk harness. It clips in the front. I found it helped to reduce lunging because it will cause them to spin around and face you.