how do i make those nifty auto-MGs in maps? like in avalanche the spawn protectors

i searched "spawn protection" in Mapping forums. he is the results list:

http://www.dayofdefeat.net/forums/search.php?s=&action=showresults&searchid=498351&sortby=lastpost&sortorder=descending

in particular, try this thread:
http://www.dayofdefeat.net/forums/showthread.php?s=&threadid=33036&highlight=spawn+protection

thanks! i may end up showing you guys what its for, depends if my... bosses let me :-P