First off, he isn't visiting the sites on accident.
I would just put a blocker program on your system rather than spy on your kid. I can tell you right now what he is viewing, and depending on how old he is, I did the exact same thing, as do the vast majority of kids. (boys at least)
If you do spy on him, he will not like you very much when he finds out AND he will look at the questionable material at friends' houses. If you block access instead of spying, he will just look at the material at friends' houses.
There is really no way to win completely. Just be glad he likes girls if that is the case I guess.
