My mates horse rears or bronks when she mounts, so she started lunging him before she mounts now.
But the other day on a hack he started prancing side ways and went verticle nearly flipping on to himself. Any ideas why he does either of them and how to stop him?
I think we need more details on this one. Did the pony just start rearing when being mounted, or is this something has its been doing since day one of ownership? Were there any environmental factors that may have caused the money to react the way it did while on the hack? How was your friend riding at the time? How has the pony been on hacks before? Did it show any signs of bad behavior before this occured? Have you ruled out pain? Tack fit, sore back, sore mouth?
Ponies are smart and you need to prove that you have more smarts that it does. He's likely pulled the bucking act with mounting long before your mate acquired him. If possible get him bending in circles immediately and moving his hip around. Pretty hard to buck when he's doing that. Keep him circling tight until he's begging to stop and only then allow him to straigthen out and walk forward. If he tries again, bend the other way. It may take a few times for him to figure out that his bucking results in this very tiring work. His body is designed for a fast sprint with his body being in a straight line. As for the rearing on the trail, I suspect he'd decided he was far enough away from home and had no plans of going any farther. Before he rears he will give off signals that he's thinking something up. That's the time to do the circles, which he is now familiar with or dismount for safety. By tight circles his head should be bent to the rider's knee with the heel driving the hips around. In order to rear a horse has to be fairly square, his body will bunch as he rocks back in order to elevate the front end. The tight circles diffuses that.