There is something else that we can use for secret communications and that is ... (don't laugh, I'm serious) - water pipes. Many places still use metal pipes, thru which radio waves can travel quite well. I read an article in a science magazine a few weeks ago, where a team of researchers were tracking various electromagnetic emissions in residential households. They fould that a lot of background magnetic fields and radio emissions were coming from the water pipes. When the neighbors used certain appliances, they could detect it because the EM emmissions were picked up and carried by the metal water pipes. And that's was just background noise. Imagine what we could transmit by intentionally broadcasting signals thru the metal pipes! Also, most of the "noise" was low frequency, and since our transmitters would be high frequency, it would probably work pretty well (unless, of course, you had plastic pipes). Most of the local net traffic could be handled thru the pipe-network, while the radio transmitters, lasers & microwave stuff could be used for longer distance stuff.