Jump gates with off switches Edit
According to the article, "Jumpgates require an enormous amount of power and cannot simply be shut down to prevent intruders. In fact it takes at least two days to safely power down a gate and another four or five to power up again."
However, in Season 1 of the show, in the episode Signs and Portents, the Raiders steal "The Eye" - an ancient Centauri artifact that symbolizes the first Emperor. At first, the Raiders "abduct" Lord Kiero, the Centauri lord who retrieved the artifact. As he reaches the command deck after witnessing the abduction, Sinclair is informed that the ship is attempting to activate jumpgate sequence. His response is to send Garabaldi and some Star Furies after them (while Ivanova is off leading the other squadron on a wild goose chase due to the Raiders' duplicity.), then he says "The ship's too small to make its own jump point, and with our jumpgate closed, the nearest one is six light-months away; and Garabaldi at his back, we've got him boxed in on all sides" [sic]. After the Raiders bring in a carrier ship capable of forming its own jump points, Ivanova is able to return through the jumpgate without recieving authorization.
These two statements appear to be contradictory. The conclusion I suggest is that while it may not be possible to simply turn the jump gate off, it might be possible to disable its ability to form a jump point by using some manner of command code. For instance, the Babylon 5 Jumpgate could be designed to recieve only activation commands from the Command deck, or it may be possible to lock access to the computer that controls outgoing jump point formation. While useful for policing the region, like in the Signs and Portents episode, it seems reasonable that it would be much more difficult (or impossible) to disable access to the gate from hyperspace. As I recall, we never see the hyperspace side of a jump gate - very few episodes show us what hyperspace looks like at all. Perhaps there is a physical (in some sense) gate positioned in hyperspace that has some means of linking to its realspace counterpart. While both sides could probably be set up to require authentication codes, the hyperspace side gate is trapped on the side where your potential enemies will be arriving. It's a fairly standard idea in cryptography that every encryption, authentication code or password can be broken given a sufficient amount of time. If that still applies, this authentication requirement would be no serious deterrant to a determined attacker. I suggest that the safe power-down and power-up sequence is required to safely establish, or break, the link between the two halves of a jump gate. This would also help explain, in part, why they are relatively rare. Not only is it made up of a fairly rare and expensive material, but also setting one up would be a non-trivial process. I would imagine that constructing something in hyperspace could be a difficult proposition.