Tools>>Internet Options>>Content--ContentAdvisor>>Settings(modify)--Enable.
If websites aren't rated and ContentAdvisor is on, then access is denied. So it seems that even if websites that don't label themselves for whatever reason still won't be seen if parents would simply utilize the tools that have been available for years.
Another thought for adult type sites that are not blocked by 'NetGear' type filtering(which is pretty simple as it uses and blocks specific strings within a URL)
Instead of using
www.thehun.com(just an example domain without any 'adult' words within it), it would be simple to add to/change the 'www' to another adult word, say like 'adult' with a simple mod of the server config.
So now instead of
www.thehun.com it could be adult.thehun.com, which would help some of the simplest filtering technologies.
Then one might also be able to use software utilized by sites like WebmasterWorld. They allow Google to spider all this content on their sites which allows them to be found within the search index. But when coming from outside links you are required to login or join in order to see it. In the typical link type site that join/login could simply be an age verification type deallybob.