sebastian wrote:
>>> Correct me if I'm wrong, but if user left his site, and then returned
> refer would point to the other site. So detecting refer value could
> possibly help the problem.
>
> Great, I'll try that out then.

Just to make sure we talk about the same. Refer header will contain the
other site url, if users comes from other site. If he hits back button
it won't work. Only with links.

best regards
Piotr N