WIreless security improvements with better antennas
If a WiFi hacker can't get your signal, he can't hack your system. That's why many power users are adding these kinds of passive reflectors to limit where their WiFi signal goes to within their home or office.
Green Bay Professional Packet Radio. Includes relevant FCC regulations on power and antennas, so you know when you must reduce power to compensate for that very high gain antenna... but you're still ahaead of the game if you do.
Aluminum foil, cut-up can or wire mesh antenna reflectors.