When you enter the site it put in a code similar to this at the top
Code:
<script>
<!--
document.cookie='atref=noref$#; path=/;'
// -->
</script>
I am using the script on
www.acalinks.com where you can check out a live example (just view source).
I do have webalizer but oh my god that seems so outdated and I can only see the top30 referers by URL (not domain)