When u access a link, u have to click again if the requesting user does not stay in the local domain.
e.g http://www.ddth.com/forumdisplay.php?f=173
They say they use .htaccess. How to ?
Thank

you can use $_SERVER var named HTTP_REFERER to get the url refering you to next link click.
all that you have to do next is to put some script into some hook loaded @ each page, and check the refer link to validate domain, then you could just easily decide whether to put another page requesting 2nd clikc or anything else you may want ;)

read syntax & docs of command @ http://il.php.net/reserved.variables

How to put some script into some hook loaded @ each page ? I don't know php...Can you help me ?

Note
They say they use .htaccess...