BlackLabbie:Ok....I need some help for a second here, please....
Apollo already knows how to sit automatically when we're walking (if I stop he plops)....should I click & treat this?
Also, since I took the prong off he pulls on the leash and it seems like we're back to square one with his leash reactiveness towards dogs. I was putting the prong on, but hooking it to a regular collar, so we weren't using it but it was on. How do I get him to heel with click & treat if wants nothing to do with the treat while we're walking (I brought come cheese with me today on our walk, which he LOVES, but still didn't want it while heeling)? Also, he pays zero attention to me now when a dog is passing, since the prong is off.
Anybody else have a tough time clicking & treating with a leash and baggies of treats?!
You need a bum bag (fanny pack??) 
Or a couple extra pairs of hands!
Does he not want food at all while he is walking or is it just while he is around other dogs?
You may need to up the ante treatwise (cooked chicken? beef? liver cake?) OR maybe you have a dog who is more toy motivated... in which case you need to confiscate his favourite toy, increase its value by playing short and highly exciting games with it and then use it as a reward during training.
Now, if he just doesn't really want food while he is around his "trigger" (in his case, other dogs, right?) then this to me is a signal that you are starting off too close. He needs to be further from the trigger for the treats (or possibly the toy) to have any value. If he is too close, then he doesn;t want to let his guard down to eat or play.
What I would do is, I would start off using the clicker to teach him to walk next to you. DON'T use a cue at this stage. Start off in and around your house, off lead. Just click him for standing beside you. Move around so he realises its for standing BY you and not standing in that spot. Now you need to add a lead. Try using a completely new collar and lead. Don't hold the lead. Let it drag on the floor. CT him for standing beside you and walking beside you. Take one step, four steps, two steps, five steps, one step, six steps..... in other words, gradually increasing, but still random to keep him on his toes.
Now progress to holding the lead and going very short distances.... maybe as far as your front door at first, then maybe halfway down your street. Don't think of it as a "walk". Think of it as a lesson, an extension of what you have been doing in and around the house and be prepared to build on it gradually.
When you see other dogs, your initial response should be to keep far away from them. Give them as wide a berth as possible so you give your dog every chance to succeed. CT for calm and relaxed behaviour, JACKPOT if he focuses on you
"Give a man a fire and he's warm for a day, but set fire to him and he's warm for the rest of his life." (Pratchett, Jingo)
"I used to look at [my dog] Smokey and think, 'If you were a little smarter you could tell me what you were thinking,' and he'd look at me like he was saying, 'If you were a little smarter, I wouldn't have to.'" - Fred Jungclaus