How do we keep our kids from being so oversexualized?

I have a teenager and a toddler (both girls). I feel like there is soooo much pressure on beauty and looks. Everywhere you look, TV, radio, internet, sex is EVERYWHERE. I mean I want to cover my kids eyes from some commercials!! I monitor my daughters internet use, but I'm not around all the time and she spends time at friends house. I can't chain her to her room, but I know she's being exposed to more than I know. I mean, all kids have to do is open the internet, and they can see every kind of porn ever thought of. I'm trying to teach my daughter morals and keep her educated about the dangers of sex, but I'm only so powerful. I give her freedom but I worry so much. You can't be too strict because then they hate you and do things behind your back, but you can't be too lenient, because they'll end up pregnant, on drugs, or worse. Anyone have the same concerns?? Anyone have some good advice?