Placing Image behind sidebar that overflows on right margin

I am trying to place an image behind the sidebar. This image is a spiral and it flows off of the edge of the page. I have the image placed, but it moves when I widen and narrow my browser window. I want it to be positioned half on the page and half over the edge, and I want it to move with the page as I widen and narrow the browser window.

You can see it at: http://www.bodysacred.sezgintester.us/

Thanks!