How to check if a webpage is visited through another webpage

Hi everyone,
I have a need to check if a webpage is visited through another designated webpage.
Here is the senario:
The main site is site-a.com/index.html
and there is a secret page site-a.com/secret.html
There is no link from site-a.com/index.html to secret.html
Then, there is another website site-b/index.html and there is a link on this page to site-a.com/secret.html
I want to make sure that users can only access secret.html via site-b.com, not via typing/refreshing/bookmarking the URL site-a.com/secret.html.
I guess, in this secret page, I need a way to check if this secret page is called from site-b.com. Anyone has ideas how to accomplish this?

Thanks.

Set up google analytics in your pages and set goals to match what you have described.

Scott, something else you can use is called Statcounter (http://www.statcounter.com). Statcounter has a simpler interface, and I used it on my sites where I need to collect basic information like visitors and page impressions. It does track referrals, too.

OK.
But if the visitor does not get to my site-a.com/secret.html via the designated site (in my example, site-b.com), I want to reject it by re-direct it to an error page.
Can Google analytics or Statcounter accomplish this?
Thanks.

No, the Analytics program only measures - it cannot take any actions. What you are trying to accomplish can probably be done through a .htaccess file. I am not 100% certain on this, but I would definitely recommend looking into it.

Look into memcached. You can use memcached as a session storage facility across multiple domains.