[eccod]

I can set the .htaccess file to only allow referrals that come from my domain, I think.

The perl script my dad wrote me (I'm not good in perl) is pretty cool.
There's an entry in the .htaccess file that redirects every request to a file in that directory to the cgi file.
The cgi file then logs the referral, and if it's not from my domain (or if it's a direct request), it delivers a different file.
I think that's pretty much what you're describing.