App Locker II android app protect your private app by fake crash. When launching a protected app, it will throw a fake crash error which may mislead guest user into thinking that your app has a glitch or something.
[androidqrcode: net.xdevelop.protector]So it can stop guest from using your protected app in a natural manner. For owners, it provides several secret unlock methods to unlock it without a trace. Using this you can lock your app without accessing another stranger.
It is a free android app which require Android version 1.5 and up to run.