How can one keep a clever child from roaming into porn etc.?

Footnote I had been reading that school systems who been giving lock down computers to their students are finding that those student are having no problem getting around the locks.

My question is why did you not try to find out from her what she find so interesting on such sites and then perhaps reach some agreement with her over the matter?

Putting her web browsing into even deeper hiding seems counterproductive to me, but it seems on the other hand finding her red handed would be a wonderful chance to have a heart to heart talk with her over her sexuality and the danger and misinformation that she is likely to run into on the net and in real life for that matter.

Well there are two ways to stop them as i see it. In both ways use services like teensafe to monitor your child's activity on internet. Its up to you to monitor it secretly and caught him/her in the act and confront them. This way if they are innocent then you wont have to go through the confrontation period and your child confidence in you keeping his privacy will also be intact. Secondly if you already have solid proof that your child is involved in such ability then let him know that you are monitoring their activities on the net so that they will be restrained from abusing the use of internet.
My son is 8 year old and use internet on his tablet to download games only but i still told him that i may be monitoring his every activity to keep him away from the temptation of these things and also i have connected his amazon account with my email so whenever he download an app or game i know which one it is through email notification.

One more time he or she as even a young teenager will just get a hold of a live CD of a linux os for example and boot his or the family computer from it and all repeat all your monitoring software will be bypass.

Having open and upfront conversations in my opinion concerning the internet with your kids instead of fighting a secret cyberwar with them will turn out far better in the end in my opinion at least for teenagers.

Of course forcing the kids to learn enough computer skill to unlock say a lock down chrome computer or a window 10 computer for that matter might be helpful to them in the future.

This - I remember when computers still indexed uncached webpages back in 2000. I still get anxious when parents doesn't have to ability to put themselves above their kids where these circumstances occur. Please move to a country or state where there's proper censorship and proper communications or/and social service. I don't think this argument is still reasonable - maybe you should move somewhere else where there's less problems and violence/abuse. Boo!