How do I stop my gelding from dropping his shoulder at the canter?

Question
Shelley,
I currently ride and show Arabians, but have decided to make a go with a Morgan in the sporthorse divisions. My Morgan gelding feels fairly balanced on the straight, but when I attempt to work him on the circle or in serpentine work, he drops his shoulder. His right should is not bad and I can usually check him up to correct it, but his tendency with his left shoulder can be down right dangerous. I have worked him on the lunge and in the round pen as well as over coverlet. I am at my wits end on how to correct this problem and would love your help.
Jamie

Answer
Dear Jamie,
Well, at least you know what the problem is-  many less intuitive riders can't feel a horse dumping a shoulder. You don't mention how old this horse is, as dropping as shoulder is often the hallmark of a young, still developing horse that lacks balance. It will be a more difficult fix on an older horse who has learned to drop a shoulder as an evasion.
Anyway, a horse will usually drop a shoulder if the rider has lost the connection to the quarters. I would suggest doing some travers and renvers dressage movements at trot- this will help you to be able to maneuver his quarters. When you go back to canter, you will need to keep a strong supporting inside leg at the girth and get after him with that outside leg to control the quarters- even go so far as to take his nose a little to the outside in counter-flexion. I would also make sure that you hook him in side reins (I prefer the kind with the rubber "do-nut") with good outside rein connection while lunging.
I hope this is of some help.
Sincerely,
S. Evans