X11: Xautolock/xlock
(last edit: 2000-11-22)
                   Xautolock is a program to ..... automaticaly lock your X Window display. You can install
it from:

/usr/ports/x11/xautolock

(automaticaly) starting xautolock
All programs specified in the '~/.xautostartprograms' are started when x is started.
So if you want 'xautolock' to start you can put the following line in your '~/.xautostartprograms':

xautolock -time 10 -locker '/usr/X11R6/bin/xlock &

This will start 'xautolock' witch will start 'xlock' after a timout of 10 minutes.

man xautolock

Xautolock monitors the user activity on an X  Window  display.  If  none is detected 
within mins minutes, a program is started as specified by the -locker option.

 -time           Specifies  the  primary  timeout interval.
                 The default is 10 minutes, the minimum  is
                 1 minute, and the maximum is 1 hour.

 -locker         Specifies  the  locker  to  be  used.  The
                 default is xlock.

As you might have noticed from the above text: the actual program which locks the display
is 'xlock' so you'll have to install that one also.

xlock
You can install 'xlock' from:

/usr/ports/x11/xlockmore

The only option 'xlock' uses which I found interesting is the '-mode [screensaver]' option
which specfies a specific screensaver to use. For a full list of screensavers see 'man xlock'.