I just saw this thread. I'm glad it's here. I'm reposting from a post I did on another thread about a horse that wouldn't go forward on cue:
I am a big advocate of the judicious use of spurs. I have found that the use of spurs cuts my training time waaaaaaaaay down and gets the horse to do the right thing willingly a lot quicker than any other means. Squeeze, cluck, touch, jab. It takes about twice before it's down to squeeze. The horse's normal reaction to pain in the sides is to move forward, unless it is blocked by too tight of rein or another obstacle (then sometimes they go straight up!). A good jab with the spurs and a loose rein is nearly always productive in teaching a reluctant or lazy horse to move forward. I am thinking your horse is not ignorant as much as he is being disobedient. It's less likely that he doesn't know to go forward as much as that he just doesn't want to.
Buy a pair of inexpensive spurs that are right for your riding boots. I like those sometimes labeled "rodeo spurs". Learn how to use them gently. If you are used to pounding on the horse's sides with your legs as you try to get them to go, you will have to re-train yourself before using spurs. Also, remember that the smaller the rowel on a spur, the more aggressive the spur is. Get one with a reasonably large rowel without getting one like Clint Eastwood's. The first time you get on with spurs, gently rub them along his sides until he gets used to the idea that they are there. Then it won't be a total surprise the first time they are used.
If you do not believe in using spurs, you'll have to get used to carrying a quirt or whip around with you. In my experience, a horse who knows a spur is attached to a heel will generally respond better to a squeeze than to a whip. By using a whip, you may eventually get a horse who starts off by moving his rear to one side as he sees you raise your arm with the whip.
I have also seen instances in which a person had a horse that had the habit of "balking". It wasn't hard to see why as I watched the rider boot the horse several times, then raise her arm with a whip. The horse saw her raise the whip and lurched forward while her arm was in the air, which threw her off balance. She caught her balance by hauling back on the reins with her other hand, which jerked the horse's mouth. This horse had no idea how to keep from getting punished.
Once you get a horse trained to obey with spurs, you can normally start riding without them for most general uses. I generally use spurs when I'm trail riding, because sometimes it gets dangerous for a horse to balk at an obstacle, and I want a horse to be strictly obedient and trusting when I ask them to move forward on the trail. I recently had a horse on a trail ride in the mountains that balked at a stream crossing. We had to cross the stream several times, and each time it was a fight to get him to cross the stream. A couple times he simply jumped all the way across. After lunch I dug my spurs out of my saddle bags for the return trip. He balked at the first crossing just long enough for me to give him a quick jab with the spurs. After that one touch, it was simply "Yessir! I'll cross right here! What next?" and I had no further trouble the rest of the day.
Read more: He's so lazy