First Referer

Hello,
I want to know where my user comes from (Google, Direct, …)
I can use the <?php wp_get_referer() ?> which works, but I want to save this information during the whole stay of the user in my page. Right now the information is lost, once the user goes to a subpage.

I have 2 ideas:

– WP has a function that saves the first referer
– I save the info in a session. Does WP have some array or variable as a session already where I can save the info or how do sessions in WP work?

Thanks 🙂