There's probably a reason why Amazon started ramping up installation of fences about 5 years ago; fences that meet some US Gov't standard that requires they be able to stop a fully loaded medium duty truck traveling 50mph. What could that reason be? 

 the key is most of those are designed to stop a small group of people doing an action against it. To deter the 100s of people that do the looting like philly or chicago takes a much more serious plan.