think of shaving his stop like shaving shards off a bar of soap with a knife, getting a little at a time.
also, get him to lift and put down their feet with you. start with trying this literally one step at a time, and then give them a mental break for a couple of minutes and repeat. it takes them a while to respond like a pull toy.
you lean, they prepare to step.
you lean back starting to stop, they start to stop.
the notion of abruptly stopping and starting with that is unreasonable.
you should literally be able to when you are finished is lay the halter over your hand and it should literally be by feel, similar to dancing with a partner.