Bu şekilde dene bakalım.
$random_url = array("http://www.site.com",
"http://www.site.com/abc.html",
"http://www.site.com/asd.html",
"http://www.site.com/sdf.html");
srand(time());
$random = (rand()%3);
header("Location: ".$random_url[$random]."");