Locked?!
Do you mean like, Invulnerable, so that it can't be destroyed? there's a trigger for that in the -Destructibles.
If youi're talking Locked like Closed, Again its a trigger in the Destructiblr Section.
u can't LOCK the gates.....now, if u mean by that rpg "u need a key" thingy, u need regions and triggers for that....
place a region in front of the door in a rectangular shape, about 2cm wide.....
since i'm too lazy and busy right now to write those triggers to you, i suggest looking at warchasers map and seeing it for u'r self....