Oh no! My 7-year-old nephew picked up some foul Pinoy language from a telenovela. (TV was left on during dinner.) How should I teach him those words are bad?

Being a TV guard to kids is a tough job. Once they hear a strong word, they tend to follow. My son has picked up quite a number of those words already. The best thing is still prevention - - never let them hear those words ever again. But then, again, that's hard. So i tried this at home: I draw or demonstrate and use metaphors to get my message across. Then make him realize that saying foul words have negative consequences. But i follow up by suggesting some pleasant words in replacement of the bad ones.