Thanks! Same to you.
I suppose that if those divs became ginormous in size, then you could ech divs in their own file and include just the random one.
// some html
$max = 10;
include 'random_divs_' . rand(1, $max) . '.php';
// more html
You'd probably put the files in their own folder though. (eg: /random_divs/1.php)
There are ways of simply adding files to a folder and your script picking one at random, so negating the need for maintaining a $max -- another day, eh?