Honest answer?
None.
A good alarm system, good security practise (lock up every time you leave, always set the alarm etc) plenty of notices up (CCTV, silent alarm, floodlights) will create the better deterrent effect IMHO.
You'll never after all create an inpeneterable fortress, but what you can do is make the thieving scum someone elses problem, why would they bother and take the risks breaking into your yard when there's a much easier one down the road?
A good alarm system will not need feeding, you'll be equally protected when on holiday, and best of all, if anything does