Split test only new visitors

gistfile1.aw

<?php
     setcookie("BTDT", "1", strtotime("+30 days"));
     if(!$_COOKIE["BTDT"]) { 
          if($_GET["gclid"]) {
               switch(rand(1,3)) {
                    case 1: header("location: /a/index.php");break;
                    case 2: header("location: /a/index2.php");break;
                    case 3: header("location: /a/index3.php");break;
               }
          }
     }
?>

this will set a cookie on new visit, and if the cookie is not set, will check for a gclid from adwords for split testing landers