A.G.
Where there is a will there is a way. You need to focus on the will or in his case the why.
Have you/his father sat down and talked with him about what those sites are all about and WHY he is not allowed to go on them? The more you try and keep him from it the more he is going to try and find a way to see it. He can always go to a friends house...you will just drive yourself nuts trying to control him.
My children are still young, but remembering back to my rebellious days, if my son was going through that phase, I would have him do a report on sex and pornography. Until he completed the report no "toys" (tv, game systems, mp3, etc). He is old enough to do this. You need to set him guidelines. What is the purpose of sex, and how different people look at sex- from chastity to pornography, AND *** the ways these choices affect their lives.***
He obviously wants to know about sex and is trying to explore what that means- these websites are offering him knowledge. You need to step in and show him what you want him to know about sex. Don't try and keep it from him, just open up his mind wider then what he is looking at now. The unknown and forbidden is always more exciting.
May you and your family be blessed,
A.