Concentrate on not getting it stolen - visible deterrent is the thing. Make the thief steal another car and then you don't need to worry about tracking it
Have one of these Diskloks too - but in yellow, so very, very visible!
Brought for another car when working away from home, and parking in hotel car parks/dark streets too often.
Use it always now, as a matter of habit really; very quick and easy to use.
Not that my car is particularly worth nicking, just a right-royal pia if your car does go, particularly a modified car with expensive aftermarket parts that are very easily/quickly shifted on, and practically untraceable...
IMHO no value what-so-ever in a mobile phone/GSM based tracker in very many parts of the UK - the phone in your hand won't work (no service at all where I live!) never mind one well hidden inside your car!