I wasn't going to post on this thread since I never use spurs, but I think this is interesting and I learned a lot from you all.
I found spurs wouldn't stay well on my boot, especially with the half chaps I had, they got in the way. I am sure I just didn't have the right equipment.
I had one experience with a horse that got dull to the leg. He was a warmblood/thbd cross. A very nice horse, but lazy through and through (less he was spooking!). The more I squeezed him to get forward, the more he sucked back. I would be exhausted after a one hour lesson on him.
I took a lesson with a guest instructor once and she pointed out something really interesting about this horse.
She said that he resented the squeezing, and this was common with horses. Squeezing, especially if you find yourself getting further and further back , makes the horse brace up against it and he loses forward momentum in rigidity.
She said, "flutter your ankle against his side". She told me to keep my foot right where it was for posting, and just flutter it from the ankle (keep sole of foot parallet to ground) and back and forth with a little bumping of his side. Liken it to "fluffin up a pillow".
Of course, it wasn't like magic. Rhett didn't suddenly jump to it, Yes Ma'am. He'd been tuning me out for some time, so he had to have the "lesson of the leg". She got on him. (with a whip) asked once with a nudge, once with a flutter and WHAM! Laid that whip on him. He jumped 12 feet forward. Then, next time she asked once with a light flutter, one tap with a whip and them immediately tap TAp TAPPPPP! And he leaped forward. After that, all it took was the flutter or nudge of the ankle. But , I had to be vigilant to correct him quickly if he was not listening to nudge, flutter. So, the rider gets what they expect. If I expect quick obediance, I will get it, but I have to expect that I will get it and follow through (and be prepared for a possibly scary reaction by horse)
I would be afraid that a horse that can tune out a leg, can tune out a spur if it is used in the same way the leg was used.
That is just my opinion. I think that spurs are for horses that are already forward moving and you want to add refinement , especially with lateral work.
Oh , yeah another thing about this lesson of the leg. She said do it from the second you are in the saddle. So, you get on, you ask for him to walk out, he slugs along at snails pace for one or at most two steps. Let him have it!
You are a new YOU! And he has to wake up and join the party.