How close do you live to other people? Wireless can only go about 300ft. MAX, as far as I know, and that gets drastically reduced as you go through stucco and wood and concrete. Wireless networks are safe, by definition, as long as no one is within the proximity to steal your bandwidth. Your dad sounds paranoid, but then again, I don't know your situation here.
Like everyone else said, you can use ethernet cables to rout from your router/modem to your computer and that might be an even better option in the future as the CAT5 ethernet cables are soon going to be able to carry much more than just internet signals (HD video, sound, internet, tv) -->http://www.tomshardware.com/news/ethernet-cable-hdmi-displayport-hdbaset,10784.html