What security measures do you think would protect against someone installing a keylogger or extracting saved passwords from your browser data files if you let t

What security measures do you think would protect against someone installing a keylogger or extracting saved passwords from your browser data files if you let them use your computer? Also, are you envisioning setting up a new, non-administrative user account for that person, or just logging on using your own account and then handing over the keyboard and mouse like most people would do?