Tricky question - referrer from ousite, or from intern?

Hi there, I have a tricky problem which I honestly think is not possible to solve. However maybe I am wrong. As you all know it is possible on php.net to pass a function name just behind the adress (e.G. php.net/function-name) this will redirct to the propper page. I did the same thing with member sites (e.G server.com/member-name) Now I am starting a referrer programm. Every member who follows a link like from anywhere on the net and registeres will be tracked and the referrer gets a point. Now I did forget that I do have several of this links on my site itself :-) Which means that they have been aquired on my site by accident :-) My question is how can I make sure that they do come from outside and are not surfing my site already. I do set a coockie as soon as someone enteres this adress, but it would be fantastic if I could do a if statement on something to make sure he does not come from my own site. I would like to keep all the links like that, just to find a way to track the origin of the user. Thank you so much for any idea on this tricky task, Andy