add_action('template_redirect', 'custom_redirect_url');

function custom_redirect_url() {

    $urls[] = "http://www.originalsite.com/site.php";
    $urls[] = "http://www.redirect1.com";
    $urls[] = "http://www.redirect2.com";
    $urls[] = "http://www.originalsite.com/site.php";

    srand ((double) microtime( )*1000000);
    $random = rand(0,count($urls)-1);
    $url = $urls[$random];

    // adapt your % redirect here if original isnt yours
    wp_redirect($url, 301);
    exit();
}