Securing the Smart Grid

I'm doubtful that any 'security' system will be able to withstand the hacker attacks that will surely be directed against the smart grid. The prize (shutting down the electricity supply) is just too attractive. The communications network for controlling the grid should be a stand alone system, with no connection to the internet. As long as we're stringing thousands of miles of high tension wires, couldn't we just include one more dedicated 'wire' for the sensor/control circuit?