$_SERVER['HTTP_REFERER'] not working in conjunction with 301 re-route

[halfasleeps]

I have this in place on every page to track where users found us from:

if(!isset($_SESSION['referal'])){
    $web_referal = $_SERVER['HTTP_REFERER']; 
    $web_referal = parse_url($web_referal);
    if($web_referal['host'] != 'www.kranichs.com'){
        $_SESSION['referal'] = $web_referal['scheme'].'://'.$web_referal['host'].$web_referal['path'].'?'.$web_referal['query'];
    }
    if($_GET['tracking']){
        $_SESSION['tracking'] = $_GET['tracking'];
    }else{
        $_SESSION['tracking'] = 'none';
    }
} 

it works except if the first page the user hits on our site is a 301-re-route it gets lost

for instance:
if they go from google strait to page A and page A has a 301-re-route to page B....then the referal information gets lost.

I believe because page A is refered from google but never gets a change to run the code and gets directly re-routed to page B and then when page B runs the code it wasnt refered from google it was adjusted in the server...

Does anyone know how I can fix this?

THANKS!

[Ernie1]

you shouldn't rely on HTTP_REFERER I can disable referrer logging in my browser, try QUERY_STRING