My goal for this off season was/is to improve my seat and get more in sync with my horse. A few months ago, I spotted this book called Balance in Movement. It goes very into depth about all the body parts, what they do and how they relate to each other. It shows how ludicrous it is to just tell a student shoulders back or heels down without correcting anything else. I've since read it several times and have felt my lower back actually start to move while riding and am finding myself much deeper into the tack due to my new found supple pelvis.
Today we had an unusually warm day for January. My horse was being a goof and somewhat naughty. Long story short, at the end of our trail ride, he decided he wanted to get home right now, and tried to take off with me on a straight narrow trail. When I attempted the pulley rein, he threw in some monster bucks and airs above the ground as it was described to me by the rider behind me. My butt never left contact with the saddle to the point where I surprised myself. I was able to stop his tantrum and get him under control. I'm sure a few months ago, with my rigid back, I would have been bucked into next week, but I am really impressed with how much this book is doing to my overall riding. I highly recommend it to anyone looking to work on their seat on a limited budget.