Multiple cables routed via very different paths. For example, Finland also has connectivity through Sweden and Estonia. Finland could lay more cables to Sweden

Multiple cables routed via very different paths. For example, Finland also has connectivity through Sweden and Estonia. Finland could lay more cables to Sweden in the Gulf of Bothnia, there's very little reason for large Russian ships to be there. Increased spending on "unused" capacity via slightly higher-latency links (so less commercially desirable, in normal times), so you can fall back on those if needed. Improved seafloor cable technology, perhaps means of burying the cable for shelter, perhaps better means of repairing them in-place. More secrecy on the exact locations of the cables? Not sure if this is realistic. Slight bias away from sea cables, where realistic. More research into high bandwidth microwave transmission? The islands between Finland and Sweden are close enough to each other that horizon distance might not ruin that. SpaceX making a bunch of money, others making a lot of noise about competing constellations.