How can i track another user account on my computer?

Hello,
I have a mini Toshiba laptop nb205 notebook and i am the owner.I created another user account(not the guest account) for friends and such to use. I know they are limited to certain things on there account because i gave the user account certain limitations, but seems like everytime a friend is done using my puter they have mysteriously changed my settings around and whatever else but i cant figure out what it is. My question to everyone is how can i get a log of what the user account does in detail so i know exactly everything they do? This will help solve my problem.