IF they actually work. I have my doubts, though.
I do facility security for a living..for 170 or so large facility clients...I can tell you it does work for those that have them around the perimeter.
Beatable for those prepared in advance, and high maintenance at times, but the Civil War buffs here on FR will tell you what a simple picket fence strategically placed in the middle of a field can do to put a monkey wrench in the plans of advancing enemy invaders.