Re the Kerch strait bridge, sabotage would be a great option. The Ukrainians could even offer a bounty (if they haven't done so already) to tempt any disaffected Russians - a million Dollars, a new identity to anyone plus a place in history for anyone who could drop a span.
One does wonder how on-the-game the various troops are who are guarding it? Its one long, windswept ol' bridge - the hours must just drag by...