example.com/proxy/*
(of course, the URLs could be camouflaged to look like real ones... eg:
http://example.com/a-very-legit-looking-article
The point was that all URLs get encrypted/replaced at the proxy. If you load the page and block all of them, you get not only a page that doesn't work, you also lose access to all other pages on the site.
This is an extremely rude way to run a website; it completely betrays your contempt for and mistrust of the client. Given that quite a few websites already demonstrate this with their malicious and purposfully-misleading ads, I expect they won't think twice about capturing all URLs with a proxy (or similar technique).
Incidentally, this type of method could be extended very easily to prevent all deep linking. Also note that this isn't theoretical. I saw this done in... 1998/1999. It had problems and was expensive to run on the server, but I suspect Moore's law has easily had enough time to solve that problem.
Its an arms race, as always. And just as the media industry couldn't beat piracy, ad networks aren't going to beat blockers, even if it means content producers get their content stripped and distributed via other channels.