[Ichneumon]

In fact, the place to "splice in" is at these repeaters since there is no need to splice the fiber at all. Instead, you tap in to the repeater's electronics.

Would you even need to "splice into" the electronics directly? Wouldn't there be enough RF leakage to pick it up just by parking an appropriate antenna next to the repeater?

[eno_]

Wouldn't there be enough RF leakage to pick it up just by parking an appropriate antenna next to the repeater?

The body of the repeater is pretty heavy-duty metal, and any RFI that could be used to pick up the signal on the cable won't travel through salt water. Possibly possibly the power conductor in the cable could pick this up and carry it out of the repeater. Maybe something could be glued onto the cable?