PHP Document Expired

Question

I doing some PHP coding, if the 'Back' button is pressed on the browser, I get the following error:

Document Expired This document is no longer available. 

What code can I implement to cater to this situation

Answer 1

Add this in the start of PHP codes:

ini_set('session.cache_limiter','public'); session_cache_limiter(false); 

Answer 2

Set Cache-Control header in your main page.

<?php header('Cache-Control: max-age=900'); ?>