Not really practical advice as I expect you already use the usual deterrents like locking as best you can, but I've had
VanBitz Strikeback/Growler fitted to two vans now, it has an external protection loop, two fly leads you plug into a socket and fix around a bike or any other item, if it's broken the alarm is activated.
It's another deterrent and I'm not sure how many people take any notice of alarms these days, having said that Growler has 5 sirens and it is
LOUD and very uncomfortable to be near when activated.