I think it gives some owners a false sense of security to have a fenced yard. Not that they are bad or anything but it's just not safe to leave a dog alone in a backyard anymore. The news reports say that many of these dogs are taken out of people's backyards. Who ever thought a little dog would become something you need extra security for?
Several years back we had to guard all dogs because people would come and steal them out of yards and sell them to laboratories. Seems like there is always some way people can use pets to make easy money.