There are numerous amateur deterrents you can fit to a car, that may or may not work, however, you have to consider the inadvertent triggering whilst in the car
All well and good, rigging car with flares, in every cavity, so car billows red smoke, if stolen, but should you lock keys in car, you're potentially shafted, or Mr AA man is
mobile phone style tracker wired up, and in the bodywork, is a start, however it will be found when they are stripping, so would potentially give small window of opportunity. Spark plug in petrol tank, coil wired to a silent alarm, hey you might not get your car back, but you can then go to the burns unit, and ask them why they tried to nick your car.