your gonna want to try to pretend like your sitting in a chair... thats what I do at least. That way your wieght will stay centered while your still leaning back. IF you just try to lean back then you will either slide off the rail fowards.. which makes you come off switch, or you will fall on the rail and slide it with some sort of body part. It sounds like you may just be pushing your weight back which will make your skis slide foward off the rail. Try the sitting thing, and take it a little at a time. Boxes are the best to try it on because you can get on them like if you were gonna slide it midsole, and the sort of move your skis out for a press... hopefully that all makes sense, and gl