preg_replace question

I found this nice preg_replace function that replaces all occurrences of an HTML anchor (<a href=...) with a link to another PHP script that log the link and then sends the user on his merry way to the the appropriate page/site: preg_replace( "#<a href=(\"|')http://([^\"']+)(\"|')#ime", '"<a href=\"/exit.php?url=".base64_encode(\'\\2\')."\""', $originalLink ); I'd like to modify this expression so that it does the same thing but *only* if the link is not to a specific page. I.e. I would like to replace all links *unless* the link was to, for example, www.mydomain.com. How can I achieve this with a regexp? I'm not very good at 'negative' regexp ... Thanks, Jean-Christian Imbeault