I would filter internet by MAC addresses aka Physical addresses this it a unique address that is built in every network card, any thing that connect to something else over Ethernet has a mac address, Laptop, desktop, Wii PS3 Xbox, iTouche ect. Your router should be able to filter out those addresses, or better yet only accept the ones your enter in. For example, your would enter in your computer MAC address to the router and tell it to block every one else. No matter where you plug your computer in it will always have access, and no matter where anyone else plugs there device in they will be blocked.
Warning on laptops most laptops have a wired connection as well as a Wireless connection. these to two separate network card so they have two separate mac addresses for each of the cards.
How is your network setup, it is two boxes one a modem and the other is the wireless router or is it just one box that does everything?
If it is two separate boxes, I would call your ISP up and ask them if they can filter mac addresses on the modem side to only allow your wireless router to connect up. That way even if they unplug the router and plug a device in directly to the modem by passing the router and it's mac filtering you still have the modem filtering Mac addresses as well.
What type of router do you have, i will see if I can download a manual for it, to see if it supports Mac filtering.