OK, well I recently started Cheyenne under english and she has been doing great with jumping pleasure, etc....for the most part. When ever we show hunt seat eq., or any of that stuff, she takes off. Being western for so long, she is highly sensitive to seat and weight adjustments, and sitting forward, it's really hard to keep her slow, at the canter, it's nearly impossible to keep it a canter. Any ideas?
It isn't about leaning forward, it's about maintaining that golden ear/shoulder/hip/heel alignment, which, with the shorter stirrups of hunt seat, means tipping a couple of degrees ahead of the vertical. In the photo anebel posted, due to the vertical position and shortened stirrups, the rider has a very slight chair seat, her heel is ahead of her hip. Granted, the horse appears to be walking. I would imagine that the rider in the pic would have to either get her leg back, or incline her shoulders slightly forward to achieve the correct alignment, or else a rising trot would be very difficult and tiring. For the alignment to be straight and vertical with hunt seat length stirrups, the position needs to be a bit ahead.
See the pic below (I don't own this photo, it's from equineformsinc.com, hopefully I correctly cited). The rider's shoulders are slightly forward, her back straight and relaxed, and with correct ear/shoulder/hip/heel alignment. No leaning, just straightness in alignment.
I can't say much, I struggle with leaning too far forward, stuck in 2 point, almost, but every hunt seat article I've ever read describes a rider position a couple of degrees ahead of the vertical (I've always been told to picture a skier going downhill, that sort of position). There's the difference between hunt seat and dressage seat (in which longer stirrups and straighter leg position allow for the even more erect posture).
All I can really suggest is to practice more forward seat. Just the same as a horse needs to learn that the application of leg asking for a sidepass or leg yield doesn't mean to go faster, your mare just needs to get the hang of not taking a lighter, more forward seat as a cue to speed up. You can sort of stiffen (for lack of a better word, this is hard to describe...) yourself, not move your seat so much with your horse to reinforce the slower pace. Although, hunt seat is a smidge faster than western pleasure (or ought to be...). Sort of move yourself the speed you want to go, slow your rising trot to slow hers, etc. Talk to her, "easy, easy," works for my greenie when he gets excited and fast (as I said, I struggle with leaning forward as a habit, I expect as I improve, so will he).
If you ride on a long rein, then the horse is free to stretch its neck.
To fast canter that's exactly what the horse needs to do - stretch its neck.
If you ride the horse with a contact to the bit, you can restrict the horse's neck.
BY leaning forwards you are cueing the horse that you are getting ready to go faster. If you want to go from rising trot to slow canter then you must sit down upright in the saddle , hesitate, keep a short rein and close contact with the mouth thru the bit and urge him on - gently. But you must restrict the amount of rein to stop him from speeding off.
At the moment he is doing what he thinks you want him to do and more to the point what you always do. He has got to be reschooled to canter slowly.
On your part you must learn to sit upright , which will fell like leaning backwards,
And you must be able to keep contact with the mouth thru the reins without jerking the bit in the horse's mouth.
You must also learn how to slow down and speed up a horse at canter.
You'll need an instructor on the ground to help you.
But it is fun learning new techniques with horses - isn't it.