Caching Secure Pages

I am having problems using sessions and caching. I have an application that requires you to log in to be able to access certain pages. The pages that require a login include a file which checks the session data and ensures that you have a valid session etc. My problem is that if the user logs out, and then goes back to these secure pages they still display as if the user was logged in. I know how to stop them caching with headers, but the problem is that if I do this, then the user cannot use their back button because the browser displays the following message : ---------------------- Warning: Page has Expired The page you requested was created using information you submitted in a form. This page is no longer available. As a security precaution, Internet Explorer does not automatically resubmit your information for you. To resubmit your information and view this Web page, click the Refresh button. ---------------------- So in summary I need a way to stop pages from caching but still allow the user to use their "back" button to go back to them as long as they are logged in. I have seen this done and it is possible some how.... Any help would be greatly appreciated.