su - userid

[grace @ nymt . reuter . com (Grace Barraza)]

Hi,
 
I know that this is not the right place, but thought that there must be
a lot of capable people who can answer this .
 
Our system administrator is not capable of distinguishing the fact of 
how to stop people from using some one else 's id.
We are running NIS+. 

The process:
 
su - root (On any client machine, of which you have the password.)
 
Now 
su - userid (You get logged in as the 'userid' specified).
 
 
Is there a way to stop this (Other than going to AFS. etc...).
 
Thanks In advance.