The teens are important years in our kids. During their teens, kids develop into adults: they develop their own worldview. Over these ~6 years, they take what they have learned and are learning and synthesize it into a view that will shape their actions and attitudes for possibly the rest of their lives. Because of this, many parents, most notably conservative Christian parents, seek to 'shelter' their kids from the world, understandably. This does make sense: expose them to too much of the world and they take the views presented by the world as their own.
However, by the time that they are at most 16, it doesn't make sense anymore. At this point, most of the framework of their worldview should have been laid. They should have a fairly clear idea of what they believe and why they believe it. And so, at this point, parents need to be concerned about the other major factor in changing their child's worldview: college. At college, their kid (by now a young adult) gets to test their worldview against the 'real world'. They find out whether what they believe actually makes sense and holds water when they apply it. Unfortunately, too many college students think that their Christian-esqe worldview doesn't actually fit reality when they get out into it.
Parents can and should work to prevent this problem. Once their child has developed a fairly firm worldview, the parents have no reason to insist on only Christian music and G-rated movies. Instead, they should be open to exposing their kids to parts of the world--within reason. Their exposure needs to be tempered with strong teaching on worldview. Parents need to teach their kids about the worldview presented in the things they are exposed to.
Now, don't get me wrong. I'm not saying buy explicit rap music and R-rated movies. I am saying to pick out the important 'classics' of their day and age--the stuff that is going to have a near-universal impact on their generation. Teach them to analyze that for worldview. They need to understand what their friends are going to believe--and why they believe it.
And you are responsible to make sure that they do.
Is this going to take work? You bet. Is that a surprise? Kids are work. You didn't have kids just so you could have free slave labor, did you?