The most effective way to protect yourself against someone using shutdown -a :
1. Pretend to be doing something really important and wait for the [censored] to use the shutdown -a
2. After you see they�ve done it take a quick look at everyone in the lab and see who is looking at you or who�s laughing.
3. Take the keyboard (preferably some really heavy old IBM keyboard), go over there and bash their [censored] teeth out with the keyboard while screaming : NO ONE SHUTS DOWN MY COMPUTER WHILE I WORK, [censored] !
This will ensure that the shutdown -a trick will never happen to you again. If you get arrested claim temporary insanity.