Best alarm system for Defender 2003

Having read stories of people wanting to pinch Defenders I'm wondering which is the best alarm that people on here are fitting to try and stop those theiving gits taking my pride and joy away!
Thank you

Ultimately, if someone really wants it, then they'll have it. Any security measures will only really serve as a deterrent and slow a thief down. Probably the most cost-effective by far is a simple isolator switch, hidden in plain sight and labelled as something inconspicuous (e.g front fog light). Combine this with a good category 1 alarm system (insurance discounts) and all but the most determined thief will most likely give up. Still doesn't stop someone lifting it onto the back of a truck though.

"Let's take this bank back to out hideout, we'll break into it later!" (The Simpsons)

The most expensive one you can afford