The current assumption is that if you're jerked to another site, you are already viewing porn... but what about the people who stumble across your site through other means?
This is what I do, it may be relatively insignificant but it's a start:
1. With the exception of one legacy site, I have a warning page on the root of my domain, which then links to tgp.html. I think it's bad news to have porn on your root page.
2. I also have <a href="http://www.icra.org/" target="_blank">ICRA</a> blocking information on both pages. You're crazy if you run an adult site without this!
To solve the first issue you may be able to use a cookie system - if the surfer has previously consented to viewing adult content, they get carried straight through to the TGP page when they load the warning page...