Session Cache

I am using session cookie to make sure that my website members login to access certain privileges. However, everytime the back button is used, the browser always RELOADS the entire page. If I remove my session in the script, the cache works well enough. How shall I fix it so that the browser does not have to reload the page everytime.

Here is the code I use at the first lines of my page:

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "">
<html xmlns="" xml:lang="en" lang="en">

the codes at the body:

<table width="750" align="center" cellpadding="0"  cellspacing="0" bgcolor="#FFFFCC"><!--DWLayoutTable-->
    <td colspan="3" bgcolor="#FFFFFF">

Thanks :jail: