"Oh. Set up the gate in an uninhabited location that would be prohibitively difficult to leave unassisted, and monitor it remotely in case anybody comes through. Then if we get any unexpected visitors they're alone on a deserted moon with no idea where you are. And you can check it at your leisure with your handy access to mortal technology. It'd be a little expensive to do it that way, but if you verify that the interplanetary portals are possible and express an interest in making some eventually, I, um, happen to be childhood friends with the emperor of this planet and could probably get him to front some extravagant aid if it means you start with us when you do get around to selling portals."