I've just started driving my horse, I've had him 5 years and done hundreds of hours of groundwork as I'm unable to ride him. I don't know his history but I am 99% sure he was broken to drive because he has taken to it like a duck to water. We've had 6 or 7 drives now out and about which I know isn't much but he's started to plunge forward violently when I ask him to walk after waiting at a junction. I don't use a whip, I have it in my hand in case but never use it. I litrally say "walk on" he knows what walk means he knows jig jog and trot on. I drive in a two wheel exercise cart, it's quite light and there's me and one other person who gets out at junctions to stand near his head if we have to wait a long time. He is fairly fit and quite strong, he's 14.2hh Welsh d type, driven in a french link snaffle. Any ideas would be great!