rotate offers/campaigns for landing page? (1)

I'm trying to setup my first campaign, got my landing page ready and I'm trying to figure out the linking to offer part.

I'm using the STM v4 tracker and setup two offers I want test as their own campaigns with 2 rotating urls in each (aff network has 2 landers). I wanted to know if there's a way so I can have the campaigns rotate evenly or would I have to grab the two urls given to me and randomly choose it myself like so:

<?php  
	$link1 = 'http://xxx/tracking202/redirect/off.php?acip=111&'.$_SERVER['QUERY_STRING']; 
	$link2 = 'http://xxx/tracking202/redirect/off.php?acip=112&'.$_SERVER['QUERY_STRING']; 
	$random = rand(1,2);
	switch($random) {
	case 1:
	   $link = $link1;
		break;	
	case 2:
	   $link = $link2;
		break;
	}
?>
	<a href="<?php echo $link; ?>">Link</a>