Thanks for your reply David! Another option (Thanks Jan Hermann) is to create a macro:
URLReferrer=="http://domain.com/"
This is very simple macro and would work only if the url matches exactly "http://domain.com/". You could use macro like this:
URLReferrer.Contains("domain.com")
To get better results, but you still rely on the referrer url variable that doesn't have to be fulfill. I would recommend to append some query string to your external links to look like:
http://domain.com/?key=lead
And then you can simply check if the query string contains that value like this:
QueryString.GetValue("key")=="lead"
Frank Daamen
LAB51 Kentico Gold Partner