Kind of interesting to see no one mention a rather obvious and more common security measure -- cameras. They are not as expensive as they used to be and if you have some networking savvy, you already have most of the equipment in your home (computer and wireless router). I can't tell you the number of times I have seen scofflaws ready to scale my fence take one look at the big Axis PTZ on the side of the house and change their minds. Remember the guy that repelled the home invaders in Phoenix a couple of years ago? He saw them coming via a camera pointing at his driveway.

Another measure that has really been incredibly effective are outdoor motion detectors. Dakota Alert makes some nice ones that can be hidden by a fake bird house. They are wireless and activate an audio tone in a receiver inside the house when someone breaks the perimeter. Different tones can be programmed to identify the location of the motion detector that is activated. These things give you an opportunity to react before the house is breached.

In short, hardening the castle is great, but I'd rather catch them before the cross the moat.