But you can trust me when I say, kids will find a way. 
And that's why, like JFC said, parents need to step it up a notch and take an actual, active role in the lives of their kids. They have to give the kids boundaries starting from an early age, and when those boundaries are crossed, they have to discipline the kids and make sure that they KNOW that what they did is the type of behaviour that will not be tolerated.
Sorry, need to rant now:
If the kids try to sneak around the rules, parents have every right to snoop through their kids' belongings. If that means going into their kids' Ipod and deleting inappropriate shit, then THAT is what the parents need to do. And don't anyone give me any of that "kid's right to privacy" bullshit. Privacy is NOT a right, it's a privelage. As long as the kids are mooching off of their parents (i.e. parents paying the bills, buying the kids' clothes, buy the kids' food, paying the kids' medical costs, etc) the kids haven't EARNED any privacy. When the kid starts paying rent, buying his/her own food/clothes/furniture/gadgets (like an Ipod), paying his/her own way through school, THEN they can have some privacy. Until then, they should be grateful that they have parents that are willing to give them free room and board. They should be grateful to not be like many of the kids in 3rd world nations who have been abandoned by their families and who are forced to live on their own, struggling to get by on scraps of food and probably never having seen more than 5 dollars in their lives.