If you want to burglar-proof your home, police have two words for you: defensive shrubbery.

Bushes, trees and vines help beautify your yard, but can also be used to deter - or aid - a criminal. The two most important factors are landscaping and lighting.

Police call it "crime prevention through environmental design," but the principles are simple. Increase visibility throughout your yard, limit access to your property, eliminate hiding spots.

Plants should be short enough to see over, trees tall enough to deter climbing - and you want to make sure the exterior of your home is well-lit at night.

Boca Raton, Fla., police officer Gwynne Friters surveys homes to help residents figure out how they can maximize security and minimize risk. On one survey, she focused on plant heights. She pointed to a bougainvillaea on the side of the home. It was beautiful, but it blocked the view from the road.

"We recommend that all bushes be shortened to 2-foot or 3-foot heights," she told the homeowner. "We don't want someone hiding behind your bushes."

Here's some tips that most police departments offer:

Trim those trees:

You want to keep your bushes (including hedges) trimmed to 2 or 3 feet tall. Taller bushes provide burglars good hiding spots. In addition, they recommend the first 7 feet of branches be pruned to prevent someone from climbing to an attic or second floor.

Also, you don't want your bushes or trees to obscure your view of your yard.

"I would take this tree down a little bit so if I'm standing here in front of your house, I can see the windows," Friters said.

Window protection:

To deter break-ins, you can plant thorny bushes under windows. Bougainvillaea, barberries and roses work well. Using gravel stones under windows eliminates a criminal's ability to silently prowl near your house. Anyone who walks on those will make a loud crunching noise with each step.

Shine a light:

Friters recommends residents install motion-activated floodlights in out-of-reach places around their homes. She said lights scare away burglars and alert homeowners to potential problems outside. Just make sure they're installed so that no one can tamper with them.