Didn't stop them from putting up a gigantic minefield and a couple a weapon platforms around their big, shiny secret jumpgate.
If they were able to keep that a secret, I'd daresay a simple buoy next to a hole in deep space wouldn't be a problem for anyone.
...
Well, now that I think about it... the minefield was common-knowledge to the New Yorkers, anyway. It's what was inside that was a secret, and no one could ever find the entrance. So maybe our solution is to put giant minefields around every Guard-hole?
Nah, I'm kidding. But hey, buoy or no, it's fine with me.