well you see jody it is that thing at the back of the cockpit, (the big round holw in the top of your boat) that looks like a seat belt .............
narkey arent you?
im just saying that you wouldnt be the first person (in this thread) who wasnt using their back rest properly. you seem to be having a lot of difficulty with the back rest, this would indicate that you arent using it properly...
if you are sure youare using it properly, as you seem to be, maybe yours is just faulty. you could try to tie a stopper knot on the rope at a point where your back rest is comfortable for you. this might help it hold better even if it is a little less adjustable.