If I had somewhere for the resulting luggage, I’d swap my saddle when parked for a nice spongy one.
Saturated with chilli oil.
Maybe with added fish hooks.
Could work on either the opportunist or as a deterrent to buying stolen bikes.
I do have a (not the flimsiest) cable lock as my second on the two tools basis. I’m suspicious of the lockless cable on a D lock approach, as the cable adds nothing once the D is broken.
My only other suggestion is the card access store or on-platform racks at the station. There’s some tailgating, but coupled with cctv has to be a riskier proposition for the thief than other racks. Worked for my commuter, but not so convenient most of the time.