Making a car difficult to steal
How about a box over the ECU and ballast so they can't power it?
That's essentially "whut." But putting it in a tight box might restrict ventilation too much.
Probably easiest to knock a hole in the firewall, install a grommet, and mount the ECU up as high in the dash as you can get. If you run an auto, you can use the unused clutch rod hole for wiring. Then break power to the ECU with a hidden switch. With the harness taped up and the ECU "up there" most thieves would not bother.
Oldmanmopar mentioned GPS. It might be even simpler, I have not "kept up." Many of you have "family" cell plans. Take one of your spare phones, set it up to track it, and disable all sounds. Some phones you can hide up under the dash and power with a battery.
LoJack is a non deal 'far's I'm concerned. There's no LoJack service around here for hundreds of miles, it's a "local thing," and if the car is towed somewhere that there's no LoJack, it won't do any good.