Most wireless routers or access points allow restrictions based on Network card internal code.
called NIC address.
Most laptops have theri wireless NIC address printed on the bottom of the laptop.
Or, just go to cmd prompt
look for the 8 part number like 00-E0-.......
put that in the wireless routers restrict ips to these NIC address and they
can see your router but never get connected.
that plus encryption via WEP should do it.