Unfortunately all the chains and locking devices in the world wont stop a thief with a cordless grinder wearing a 1mm thick blade. We use them at work to cut off high tensile 16mm bolts and it does it quickly with EASE!! Yes its noisy, but how many people are going to say something if they see a bloke (or three) using an angle grinder in the middle of the day? And if there's no one else around, all the better for the thief.
A mate of mine had a brake locking system on his EH Holden. When it was stolen using a tow truck, the thief simply cut the brake lines and that was that.
A tracking system, with no warning stickers or flashing lights, so the thief doesn't go searching for it, is probably the best bet in getting a CT back. Failing that, that's why insurance is a necessary evil.
Avo