Trying to get 2 divs not to overlap

Hi there,

I am working on a layout where I have a static vertical menu on the left and a scrollable content area on the right. When I move to a screensize below the desktop size the right hand content pane is able to scroll below the menu - how do I set it so the site does not allow scrolling (left right) at all on the content pane but still allows up down scrolling.

My preference would be that content on the right pane either gets smaller or the whole page (both columns stay fixed but the entire set scrolls.

Here is my site Read-Only: [LINK][1]