Track Adsense exits URLS and send to catch page!

Hi! I want you to create a script that can track the exit link of an adsense block. Step by step functionality. Step #1 Script catches outgoing URL of the advertiser that get clicked. Step #2 The URL is sent to my catch page. Catch page is made in PHP. There are several scripts on the internet that states they can do it but they don't work. Problem seems to be with catching the exit url, that variable never get the value. The script must work with ADSENSE (TOS: Terms of service). That means you can't alter the code provided by Google.