I saw the "button" photo on Bungie, and it is too simple. You probably want the "Torpedo Switch" combined with the gate to make it more 'button-like'. I made a map based on a switch, so I've seen them before.
that was really helpful I don't know if you do or not already but this should go on the halo 3 forums on bungie.net it would help a lot of up and coming forgers who don't know about this site
This isn't mine, i'm just the bungie reporter, but the best help i can give you is to download the map that is provided and from there you can get a better understanding of how the gate is operable.
I kind of get it, but am having trouble visualising it. From what I see though, this is a great idea!
My Maps:
Progression - Planning|Building|Testing|Done |100%| Should I post it?
Command Point - Planning|Building|Testing|Done |5%|
Ski-Brawl - Planning|Building|Testing|Done |1%|