From Russ Smith:

Okay, this is an improvement on the usual unter kill command.  Make your room
own itself, then set the following macros:

set here cmd kill = @_if "${me.hvn}" "@_echo Sorry, this is a havened room." else "Xkill $1"
set here cmd Xkill = @_if "${!1}&F" "@_echo I don\\\'t see $1 here." else "@do \"killed ${!1.nam}! ${!1.+die}\";@teleport ${!1} home"
set here cmd haven = @_if "<put your oid in here>" "@set $me str hvn T;@_echo Haven set." else "@_echo Permission denied."
set here cmd unhaven = @_if "<put your oid here>" "@set $me str hvn F;@_echo Haven unset." else "@_echo Permission denied."

Have fun!  Notice the way I tortured a boolean in Xkill.  This is because of
the following interesting truth table:

"my oid"	:	true
""		:	true
"other oid"	:	false

I originally went with that, but then you couldn't suicide. :(

"my_oid&F"	:	false
"other_oid&F"	:	false
"&F"		:	true.  why?  beats me.

It looks not entirely feature-like, but it's VERY useful for detecting
blanks!  So don't fix it, PLEASE!