How to trap !sh at keyboard

[Billy Davis]

It seems that some of  our users are inclined to key in '!sh' at the 
shell prompt, which promptly shuts down our Red Hat Enterprise 3 Server, 
interrupting everyone else's work.  Is there a line that we can add to 
the inittab file, that will trap this string, in the same fashion that 
the 'ca::ctrlaltdel:/sbin/shutdown -t3 -r now' line traps 
Ctrl-Alt-Delete inputs?

Thanks