It doesn’t help that much, but you can make a network invisible, so that you need at least one set of hacker tools to get in. For Apple Airports, here is what you do, it is really buried in the latest user interfaces:
# Launch AirPort Admin Utility. It’s in Applications/Utilities/AirPort Admin Utility.
# Select your Basestation for the list on the left
# Click Manual Setup
# Click the Wireless Tab
# Click on Wireless Options
# Check Create a closed network.
# Click on Done and then Update