Most people in the suburbs of Johannesburg and Durban have high walls and electric fences surrounding their properties. It's quite different in Cape Town though - what you see here isn't really the norm. In Cape Town you'll find that some houses are protected like fortresses and others don't even have a fence, nor a burglar alarm - some times homes in Cape Town don't even have burglar bars.
Something that I find amusing is that when people move from Johannesburg to Cape Town, one of the first things that they do is to build a palisade fence or high wall around their property. While I understand their need to feel secure, it's still just a little amusing to predict how long it will take for the security barrier to be erected. :)