I have a completely 3rd party possibility for the profane language....
I use an internet filter for my kids called Cyber Sentinel.
What I like about this program is it doesn't act as a proxy for certain programs. Other filters will only work with certain instant messengers and certain browsers and not at all with programs it doesn't know about.
This one monitors what's displayed on the screen.
So if ABCDE is a profane word, anytime that appears on the screen, whether it be in an instant messenger chat, web browser, or inside the playing now track info plugin with lyrics showing in MC.
It can be configured to shut down the program, cover the entire display area in gray, or just silently alert you that the content was viewed (including a screen shot).
You can also add words to the "dirty words" filter. So if you don't want him listening to a certain artist at all, just add the artist name to the word list.
Perhaps using atagger to fetch the ratings for all your songs, then build a view scheme that excludes those you don't want, using access control in MC (I don't know about that) would work, and then Cyber Sentinel will let you know if there are any breeches.