I think we've mostly covered physical security.
To deter ride-offs, you could insert a simple switch into the circuit powering the ignition coils. The bike would crank, but it wouldn't start, even if they tried to bump-start it.
Basically, this could be part of a "pile of crap" defense -- if they think they've got it hot-wired or broke the ignition or whatever and it doesn't start right away, they don't have time to troubleshoot or rummage around in the ignition any further. "Obviously I got the wiring right because it's cranking. Just an old nail that's hard to start. Didn't want it anyway..."
I don't understand the criminal mind at all, so maybe this is giving them more credit for thought than necessary. But one principle of website security is giving false feedback to evil-doers; waste their time and they'll give up and move on sooner. Allowing the starter and lights to work would fool them into thinking their efforts were successful but the bike has some other starting problem.
Of course, you might still return to a buggered ignition, a dead battery, and a bike pushed over on its side. And again, this would only affect ride-offs, not other methods of stealing a bike.
As I once learned with my KLR, the faint odor of cow manure is a pretty good deterrent, too.
That's hilarious!
Parking next to a newer more expensive bike makes an old GS pretty unappealing, I'd think.
We've had two stolen. A Yamaha XT225 and a little Chinese off brand scooter.