I utilized .htaccess to deny them access to my site. I also renamed the add.cgi script, just in case. I've written them two emails in the past and they never removed my site, so I had to take evasive actions.

I had previously used the "valid referer" option in the links setup, but it appears they managed to blank out their referer, either that or my site stopped reporting it.

One other thing I did is if someone who isn't on the valid referer list manages to auto-submit, I blanked out their submission information. At the very least they'll have to type it in again and this might be enough to get them to rethink whether they want to bother.