I wish I had a cure for this but I am happy to hear that I'm not the only one with this problem. I am constantly hiking myself back up into a chair to the point that I've considered installing a seat belt... come to think of it... maybe I will. But that wouldn't actually fix the problem just put a band aid on it. I tend to think it's a core strength issue that might benefit from pilates or yoga. I do try to remind myself to straighten up and purposefully breathe in deeply. Or I could try velcro on my chair and my butt.