Have you heard about Double Meta Refresh Code:
X.php
<?php echo "<meta http-equiv=\"refresh\"
content=\"0;url=y.php\">"; ?>
Y.php
<?php
$page1 = "URL #1"; $page2 = " URL #2"; $page3 = " URL
#3"; $page4 = " URL #4"; $referer =
$_SERVER['HTTP_REFERER']; $mypages = array($page1,
$page2, $page3, $page4); $myrandompage =
$mypages[mt_rand(0, count($mypages) -1)]; if($referer ==
"") { echo "<meta http-equiv=\"refresh\"
content=\"0;url=$myrandompage\">"; } else { echo "<meta
http-equiv=\"refresh\" content=\"0;url=x.php\">"; } ?>
Replace URL #z with the pages you want y.php to redirect
to.