How to put a password on only certain apps on my iPhone?

I don't particularly want a password just to enter my phone, I want it for certain apps that I don't want to be accessible to anyone else other than myself. For example, I want a password on my messages app or camera etc. And I was wondering how to do it on my iPhone, can anyone help?

Install any of these apps

http://www.google.com/...hannel=new

you have to install additional app that secures/password-protects apps