Consensus seems to be the only truly effective anti-theft device is the Ravelco
Ravelco Anti Theft Device
You can read up on it, and find related forum discussions all over the place for several years. A couple tidbits:
Ravelco claims to have 100,000 different possible "caps" .. which is the part you remove and keep in your pocket, thereby disabling a variety of circuits in the engine.
There's currently no Ravelco distibutor in the seattle area, so I submitted a "No dealer nearby" request on their website. A couple days later, the Texas outfit emailed me saying no Ravelco shops in Seattle region, but they could ship me one direct for $399 plus shipping, and have any mechanic install, suggesting it would take about 2 hours). I presume careful attention to the install instructions would be required.
I emailed a Ravelco shop near Denver CO, since I'll be passing thru there. They quoted me $499 + tax installed, and said it would be a two hour install.
Some folks (on this forum? maybe another) have installed it themselves. Try a search.
Have fun reading the user reviews of folks whose expensive vehicles were NOT stolen, but the steering column, ignition, etc were trashed in a theft attempt. One reviewer said he even caught the would be thieves red-handed, and one said he'd been trying to get it going for an hour ;-)