[Mong]

Put this code near footer

<script type="text/javascript">
function adclick() {
	if(window.status.indexOf('go to') == 0) {
		urchinTracker ('/aclick');
	}
}
	
var elements;
if(document.getElementsByTagName) {
	elements = document.body.getElementsByTagName("IFRAME");
} else if (document.body.all) {
	elements = document.body.all.tags("IFRAME");
} else {
	elements = Array();
}
	
for(var i = 0; i < elements.length; i++) {
	if(elements[i].src.indexOf('googlesyndication.com') > -1) {
		elements[i].onfocus = adclick;
	}
}
</script>

And then set www.yoursite.com/aclick as goal in analytics.
It will track approx adsense clicks