Building and maintaining the fences needed to control livestock is an expensive and time-consuming business. The materials alone can cost more than $20,000 a kilometre. On top of that, there is the cost of repairing damage caused by wild animals and falling trees. And then there is the need to move some fences around, a bit at a time, so that grazing land can be used efficiently. Strange as it may seem, many ranchers would therefore like to get rid of fences-if they could.rnAccording to Dean Anderson, an animal scientist at America's Department of Agriculture, and Daniela Rus, a computer scientist at the Massachusetts Institute of Technology, the answer is to move from real fencing to the virtual sort. The idea of virtual fencing is not entirely new. Pet "containment" systems, such as collars that give dogs a small electric shock if they roam outside a particular area, have been around since the early 1970s. But attempts to come up with a system for controlling free-ranging animals have failed.
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