Require login for Single User mode?
The following article may help your problem. :)

Mac OS X: Require Password at Single User Mode:


  By default, Mac OS X will simply give you a shell when you perform a Single User Mode startup.  However, you can force OS X to ask for a password in order to gain shell access.  To do so, vi the /etc/ttys and change secure to insecure.  Once you have done so, create a password in /etc/master.passwd for root.