Get original URL referer with PHP?

I am using $_SERVER['HTTP_REFERER']; to get the referer Url. It works as expected until the user clicks another page and the referer changes to the last page.

How do I store the original referring Url?

Store it either in a cookie (if it's acceptable for your situation), or in a session variable.

session_start();

if ( !isset( $_SESSION["origURL"] ) )
    $_SESSION["origURL"] = $_SERVER["HTTP_REFERER"];

As Johnathan Suggested, you would either want to save it in a cookie or a session.

The easier way would be to use a Session variable.

session_start();
if(!isset($_SESSION['org_referer']))
{
    $_SESSION['org_referer'] = $_SERVER['HTTP_REFERER'];
}

Put that at the top of the page, and you will always be able to access the first referer that the site visitor was directed by.

Store it in a cookie that only lasts for the current browsing session

Using Cookie as a repository of reference page is much better in most cases, as cookies will keep referrer until the browser is closed (and will keep it even if browser tab is closed), so in case if user left the page open, let's say before weekends, and returned to it after a couple of days, your session will probably be expired, but cookies are still will be there.

Put that code at the begin of a page (before any html output, as cookies will be properly set only before any echo/print):

if(!isset($_COOKIE['origin_ref']))
{
    setcookie('origin_ref', $_SERVER['HTTP_REFERER']);
}

Then you can access it later:

$var = $_COOKIE['origin_ref'];

And to addition to what @pcp suggested about escaping $_SERVER['HTTP_REFERER'], when using cookie, you may also want to escape $_COOKIE['origin_ref'] on each request.