It depends on the sense of "log out" you want. If your users use the
  'tcsh' shell you can set the autologout shell variable (and possibly
  make it read-only) in a startup script to log out inactive shells.
  This won't do anything to an instantiation of tcsh which is waiting
  for another program to quit (e.g. a 'more' process in mid-file) or to
  programs other than tcsh (e.g. a 'jot' window), and it won't log one
  out of the graphics console. One can imagine a program similar to a
  screen saver which would log one out after so many minutes of
  keyboard/mouse inactivity, but we don't know of one. However, if
  you're only worried about security (rather than resource hogging) it
  may suffice to use 'xlock' to lock the screen rather than actually
  logging one out. For that matter, tcsh can also lock itself rather
  than logging one out; this wouldn't be helpful on a graphics console
  but might be on a simple terminal.