roro said this briefly, but I would like to reiterate this very important tip:
When he stops, DO NOT turn and face him to see why he stopped. Your energy should be saying very clearly, "come with me, let's go forward!" If you turn to face him, he is reading your body language to mean "stop" "back-up" or "get out of my personal space!"
While walking, keep no tension on the lead/halter. When he stops, keep your body language moving forward and add light halter pressure to subtly cue "walk forward." If no response, keep the light pressure and add a verbal "walk" or cluck. If no response, keep the light pressure, add your verbal cue, and toss the end of your lead rope behind your back towards his hind end (remember, you're still facing forward). If still no response, do all of the above plus twirl your lead toward his rear end/mid section (however far back you can twirl it without turning your body too much or facing him). If still no response, do the above, and then let one rope twirl actually plop him on the rear/side. If he's still planted in place (hopefully not by now!) then go alpha mare on him, pin your ears, flail your arms, shove him, whatever it takes to get him to move...even if it may be sideways or a turn on the haunches or something.
At whatever point he moves, tell him he is a "good boy" in a friendly tone. (Best if he's still moving when he gets the "good boy" so he knows moving with you is the good part.)
When he stops again, start back at step one...body language forward, slight halter pressure. Keep adding the steps until he remembers, "oh yeah, if I keep standing still, she'll keep getting more aggressive, and eventually go Crazy Alpha Mare on me! Maybe I'll just walk forward now instead."
Also, don't work on leading and stopping for extended periods of time going in endless circles. You and your horse will get bored and stop learning. Throw in a couple other things to the mix: ASK him to halt, back, do some figure-8s around cones, turn on the haunches/forehand, etc.
Be very aware of your own body language while leading. You are the alpha horse, walk with authority! Picture the handlers in those showmanship classes...head held high, no doubt that the team is going where the handler wants!
Soon enough, Glyder will follow just your body language with maybe a halter pressure reminder every now and then.
Monte - 15 year old Paint/TB
Auric - 13 year old Arab