so this might be a silly suggestion but what if someone devised a way to secure the unit behind the dash properly and not just the cage? When you go behind the glovebox you can see the unit and a frame of some sort between the glovebox and the RNSE... what if the unit could be bolted onto that to make it more secure?
yes i know some will come back and argue the point of what if they damage the whole dash to get at it but the cage it sits in is hardly working to 'secure' the unit!
it doesn't take that long to get the glovebox out and get behind it but it does take alot longer than a couple minutes so for any low life thief it might stop them from actually managing to get the unit out?
of course there are aftermarket alarm systems and the pentaglass mentioned above that can also help them from getting in the car in the first place.
one extreme secure method could be to have the system hooked up with some sort of electric shocking unit that turns on when the alarm is on so that if someone attempts to steal the unit, they will be electrocuted (not to death but near enough would teach the fcuker a lesson)