LoJack is great, depending on the area where you live. If you live outside of a big city, though, it's not going to do you much good. They have a great system called early warning, where a key fob has to be in the car when it is moved/started, or they will immediately notify you by e-mail, cell, pager, whatever you'd like. If it is being moved without your wishes, you call and they start the search immediately--instead of waiting to come out and be surprised your car is gone, sometimes many hours after it was actually stolen. I think the stock system is pretty good. Put that with early warning lojack, and you've got a great combination.
You could also think about window etching, which is very inexpensive, and is another great theft deterrent. If they want to chop or otherwise illegally sell your vehicle, they've got to either ditch the glass or get new glass entirely.
I am always very sketched out by any kind of aftermarket alarm or electronics being tied into a Land Rover. If you are going to do it, get an exceptionally good guy with specific LR experience, or you may end up with a headache. Also, if you are still in warranty, I'd be a little concerned about warranty issues with the aftermarket system.
