The tweak I'm talking about is AppLocker ($.99, USD). With it, you can lock apps, folders, home screen and more. Comes with an Activator toggle or you can get an SBSettings toggle (or both).
I've not put it on my iPad3 (it really doesn't leave the house), but I've not heard that people have trouble with it. As far as I know, it works well on/with iOS 5.1.1.
There are many more features to this than the brief bit I listed. So, have a full read on Cydia.
Marilyn