one quick way you could do that is create an array of all your links, and then generate a random number between 0 and the number of links - 1 and use that number.
so like this if you had 3
Code:
<?php
$url[0] = 'http://www.fuck.you/fuckoff.html';
$url[1] = 'http://www.suckmyballs.com';
$url[2] = 'http://www.lickmynuts.com';
$fuckingNumber = strval(rand()%3);
include($url[$fuckingNumber]);
?>