The above posts are good suggestions but can become a lot of work.

- The bad part about changing you NIC config., you are changing it every time you want to get on line and when you want to dis able it.

- I think it would be easy for a young lad to figure out what cable needs to be replaced to get it working again.

I have a cable connection and I think the easiest thing to do would be remove the power cord on the modem when you want it disabled. Not exactly what you had in mind but it would also be a hard cable to replace. A CAT5 cable, or a coaxial cable can be picked up just about anywhere. The powercord on my modem is unlike any other in my house.