Trim them to the height of porches or windows. Spiky plants like cactus and other even more ferocious varieties make a great deterrent if planted under windows. Place large gauge gravel on the ground near windows. The noise caused by intruders walking on it can become a psychological deterrent. Engrave your property with identifying numbers and publicize it through decals placed in conspicuous areas, visible to any would-be burglars in your neighborhood.
Engraving makes stolen property easier to identify and harder to sell.
Make your home look occupied at all times. Leave several lights and a radio on in the house when you go out at night. Do not leave a small light in a hallway or corner to light your way back in your home, this actually works as a signal to burglars that you are not home. Turn the ringer on the telephone down low. If a burglar is around, he won't be alerted to your absence by a ringing phone.