There's essentially nothing you can do to deter this sort of behavior short of starting a war

That's exactly the appeasement mentality that lets Russia get away with everything.

"We don't want to start a war doncha know, so whenever Russia attacks us we'll just take it on the chin and not fight back too hard".

It appears the world has forgotten the lessons of the Sudetenland.

could you cut russias undersea cables in a tit for tat?