Locking MacBook to one wi-fi

At one point my machine would only see one wi-fi, ours. We're in a neighborhood with many networks visible, so secured, some not. I have out router confirgured for some parental controls, but my clever son has learned to squat on neighbors unsecured networks.

I could ask the neighbors to secure their networks, but I can't match up SSID with the neighbor, so I want to have only our network set-up in the Network preferences.

Is this possible? I've tried every combo I can think of (prompting for other networks, etc.), but I still get a full list of available networks. I could swear it used to be different, but at some point my son changing things. I'd like to do the same with his iPod as well.

Thanks for your help. I'm running a MacBook with Snow Leopard.

create a new Location, use it and Not Automatic.