So you reccommend teaching leg, then neck ? The only issue with this for us will be, and I don't know how this started, but when I have tried to use leg to cue he thinks I'm telling him to speed up and will trot. So, in that situation, I could see doing a few things... I could press back with both reins, but he may ignore that. I could ask him to one rein stop, but that's just stopping - I could teach a verbal cue on the lunge, but I'd rather not have verbal cues. Um... I will see what works. He may actually slow his gate when I squeeze both reins, actually. Any ideas, just in case? Do you think just skipping the leg cue and going right to neck has less chance of success?
I believe it's all contingent upon each other. Right now, your horse is not broke to the leg cues, so you will have to use more directional cues, even maybe over emphasizing them, until he "gets it" and then you can lessen it.
So if your horse is not used to being driven by the leg, you need to use your directional rein to open the door - give him a direction to move it. Then the leg encourages the movement into that direction.
If the horse speeds up into a trot, you will block his forward movement with your outside rein. Insist that outside leg means turn, not go forward.
All my horses have several buttons, and several combinations of buttons. Both legs squeezing at neutral position is speed up. Outside leg before the girth is move the shoulder, outside leg at the girth is sidepass, outside leg behind the girth is move the hindquarters. Everything correlates to that, no matter what I do with the head. If the horse moves forward when I only asked for a pivot, then we block with the outside rein and give him a little more "help" with the directional rein to turn.
Contrary to popular belief, you don't use the one-rein stop every time you stop. That is not the goal. But, if your horse is bucking and running off, pulling back on both reins (unless you are pulley reining), will only encourage the horse to power through the bit, and give you more powerful bucks. A horse cannot buck (well) or run off in a circle. So, if you are galloping off, a full one-rein to the thigh is not a good idea, but the horse should have the presence of mind to understand that turning that head puts him in a safe place, takes his mind off the fixation of running, and controls him into a circle.
That being said, my one rein stop is the prerequisite to stopping with no reins. I don't want to pull back on both reins to stop, because I pull back on both reins to collect my horse going forward. If I pull back on both reins, I do not want my horse to stop. I want him to collect into the bridle.
If I drop my weight and drop my reins, I want my horse to stop dead. If I wiggle my spurs, I want my horse to back up. I don't want to reinforce pulling back to signal stopping. I want my seat to be the cue. I want my horse to start to listen to my body language. If he doesn't listen to my deep seat, then I will get his attention by a one-rein. Then he realizes, hey! I forgot something. This one-rein is not fun, next time I will listen to what comes before.
Then you can speed up the disconnect with other means. But the one-rein is not something you do every single stop. It's a means of teaching the stop on no-reins.
And also, only a poorly trained horse will duck out from you. I can jog my horses with their heads flexed to the side. That does not mean they get to duck out. That's what your outside leg and rein is for.