<html>
<head>
<title>Prueba de Acortador #1</title>
</head>
<body>
<?php
// Cargar arrays con códigos de N banners
$banner[]= '<script>var adParams = {s: 1000141798, w: 728, h: 90, c: 2, blank: false}; </script><script src="//js.srcsmrtgs.com/js/ad.js"></script>';
$banner[]= '<script>var adParams = {s: 1000146845, w: 234, h: 60, c: 2, blank: false}; </script><script src="//js.srcsmrtgs.com/js/ad.js"></script>';
$banner[]= '<script>var adParams = {s: 1000159735, w: 234, h: 60, c: 2, blank: false}; </script><script src="//js.srcsmrtgs.com/js/ad.js"></script>';
....
$banner[]= 'codigo del bannerNN';
// seleccionar al azar un banner de 0 a los que sean
$r = rand(0, count($banner) -1);
// mostrar el banner
echo $banner[$r];
?>
</ul>
</body>
</html>