overflow with long left sidebar

I use layout 1c, sidebars right and left. If I add too much code to the blocks in the left sidebar, so the page gets very long, the right sidebar disappears off the left of the page. You can see its top right hand corner peeping out, just below and to the left of the bottom left hand corner of the left sidebar. Same in FF, IE8 & Chrome. Took me ages to work out the solution was removing some of the blocks from the left region!

What is the easiest fix, please?

BTW I am a big fan of Genesis, thanks!