Handling link source on a website

i am looking for a way to track link sources on my website. The idea is that a subset of links on the website carries certain identifier within it. When a link is selected, it is then handled by scripts and the identifier is passed to a third party as a parameter within newly generated link. This way I and third party know where the client came from (having this information for every individual client is important).

Now, it is easy to do this for the unique links which i have all over the site, but I am out of the ideas how to distinguish between the links in places like headers and forms. Links in headers and forms will be the same for different pages. I can potentially use duplicate forms but this will create certain mess.

Any ideas what is the best way to proceed?