So much for that thing about one foot is always on the ground. I know you can't do anything about the snow fence at this time of year, but the scoreboard detracts from the picture.
Might have been a little stronger with a blurred-out background to showcase the horse/rider a little better. I know this isn't easy with a lot of cameras, but it would have made for a little better image, I think.
Nice shot getting all fours in the air, dirt in the air, rider in the air, and the sun paints the horse's muscles perfectly. If you had used a slower shutter speed and panned some motion blur into the background while keeping the horse and rider in focus you would have won this challenge. If you spend allot of time at the track - I would deffinitly practice and perfect the panning technique. Another sudgestion is always try to find a spot where your picture will capture the track name - you could get lucky and catch a picture that is marketable.