It's like racoons and trash cans...
The absolute best you can do is make it such a hassle that they go to the neighbors instead.
But eventually the neighbors racoon proof better than you did, and now smarter more motivated racoons show up and figure it out, restarting the cycle.
You'll never keep racoons away from trash, and you'll never keep highschoolers away from porn.
On the flip side, circumventing this is one of the only ways they get to learn critical thinking. And they'll grow up into adults that know how to circumvent shit like this.
This will be like DARE and a giant backfire. But instead of kids underestimating cocaine, they'll get some computer skills at least.