See, if my horse doesn't lope off as soon as I ask, I pull his butt into the ground, spank his butt all the while containing him then I walk a few steps scoring him (rounded, soft on the bit) and ask again LIGHTLY.....he WILL decide that 'hey last time I didn't lope off sucked, this time I WANT to lope off straight away.
your horse (according to behavioural science) is more likely to decide "hey last time I was asked to lope off I ended up being stopped and spanked, while my natural response to spanking, which would've probably been to lope off, was withheld. Loping off must the wrong response to the original cue"
Also if your horse was finished and knew his job he would do his job without needing to be spanked into it. Nothing against spanking, and nothing against your horse, that's just how it is. Horses do what they know to do to relieve pressure. And if they are asked to lope, yet get that relief of pressure after having not loped (not loping includes having their "butt pulled into the ground"), they're simply going to be less likely to lope again in future.
Cherie, here is a parallel that I suspect you'll understand: a horse that, when asked to canter from a trot, will keep trotting faster. What would you do in that case? Probably the same as what i've seen you advise to countless others, which is to "over/under" their butt into gear and really get them going into a fast canter or even gallop, instead of just "begging" them to canter. You probably wouldn't "not let them go forward at all" in that case, so why do you advise it in this case? Especially seeing as though both OPs problem and a horse that will trot faster instead of cantering are essentially different symptoms of the same problem - not enough forward impulsion.
So what I don't get is why holding them back while you "spur the hard 4 or 5 times or 'over and under the horse several times -- hard" will work any better than spurring or over & undering them, but letting them find that promptly going forward will relieve them of that, thus solving the problem.
Also I just read this while I was typing:
On the getting after a horse for not listening to leg aids --- the reason you hold the horse back or abruptly bring him back to the place where you are again asking for the response is so that you can immediately ask with a light aid and 9 times out of ten, he will respond correctly. The 'over-haul' is to get his attention and make him WANT to listen for the light aid -- which he will do. He will respond with the best transition that he has been trained to do where nagging just gets increasingly poor transitions.
I understand why you might take the horse back to where the original problem happened & get a better transition there, and I understand why the "over-haul" works, but to somewhat negate the effectiveness of the 'over-haul' for the sake of keeping the horse in the same spot it originally gave a dull transition seems counter-productive.