[GauntletWizard]

In international waters, you still own your boat; The cables are owned by the company who laid them, under the sovereignty of their country of charter, with provision to international law regarding telecommunications and maritime navigation.

The biggest thing stopping multiple countries from tapping the same fibers is signal strength; I imagine that it becomes obvious that you've got a 'leak' after just a few splices. The other thing is that few countries posess the technology to pull off an undersea cable tap; There's only one USS Jimmy Carter, and I don't think the US loans it out, and while I'm certain that China, Russia, and some of the major European states have their equivalents, I doubt the list is very long.

None of this matters in context of the article, of course; Glimmerglass's technology seems to mostly live on the ends of these cables, in the comms cabinets just onshore where the cables emerge. There, you can tap as much as you want, so long as you're the sovereign. They simply wave a national security letter or equivalent in the face of the telco, and they've got a rack next to the cables doing whatever it is they want to do.