Page template to check referring page and redirect

<?php
/*
Template Name: Check Referer
*/
/*
   http://www.gravityhelp.com/forums/topic/lock-down-a-page-unless-you-complete-a-form
*/
// if the current user cannot edit posts, they might not be logged in, or might be logged in as subscriber
// which is the only role which does not have edit_posts capability.  This is so editors and administrators
// can directly access the page to make edits, without having to submit the form to set the HTTP_REFERER
if(!current_user_can('edit_posts')) {
    // define the URL where we want to send people instead of showing them the page they requested
    $url = trailingslashit(get_bloginfo('url'));    // can be any URL.  This is the URL for the home page of the site
    // define the URL you want to make sure people come from before gaining access to this protected page
    $check_url = 'http://www.example.com/page-on-your-site/that-people-must-come-from/';
    // if the current user is not logged in with more than a subscriber role, check to see if HTTP_REFERER is set
    // make sure HTTP_REFERER is set before trying to read the value; avoid PHP warnings and notices
    if(isset($_SERVER['HTTP_REFERER'])) {
        $referring = $_SERVER['HTTP_REFERER'];
        if ($check_url <> $referring) {
            header("Location: $url");
            // don't process any more code
            exit;
        }
    }
    // if HTTP_REFERER is not set, redirect to $url as well.  This may be overly aggressive
    else {
        header("Location: $url");
        // don't process any more code
        exit;
    }
}
?>