As and when I am in that situation, there will be the communal use of the computer (which will have the best I can do in terms of lock down), but until they are old enough/responsible enough to have a pc in their room they won't get that option.
Kids are resourceful and will undoubtedly work a way round it - but as long as the casual browsing is blocked then that's what would help.
Then again we didn't get internet until I was 15/16 anyway, even then it was dial up and slow. Sure, I looked for it, but at the time only a few fairly low quality/soft pictures were available.
There's so much hardcore, streaming availability out there that I don't particularly think it's sensible for young impressionable children to be subjected to. There's nothing wrong with sex at all, in fact I think we're all agree you can't get too much of it... however, having it so gratuitously available to young persons is not always going to be sensible. Of course this doesn't apply to everyone as everyone has been brought up differently and so on. Of course, if the children are brought up with the correct understanding and are sensible in their approach to it, then of course there's nothing "wrong" with it per se, and I'm about as far from a prude as you can get - I just still believe kids should retain their innocence as long as they can. Everyone is too much in a rush to grow up these days.