BOSS Search - filtering out adult sites

Hi folks,
I' m using the filter option -porn to filter out adult sites, but I still see obscene results in the search results. (try the term xxx videos)

Upon comparison with google, it looks like they have a different approach to filtering and was wondering if that has any merit / feasible.

In Google, If I do a search for [xxx videos], with safe search on, the query is run as follows: [-xxx videos]
In Yahoo, not sure how filtering happens internally, but it looks like yahoo can successfully filter out obscene sites if a single keyword is used, (eg., xxx , porn) - but not when multiple keywords are used.

As a work around, I can look for terms such as "porn, xxx" and modify the query to "-porn" , but that would mean a lot of special cases..

Hoping someone can shed some more light on this topic.