WPA2 is extremely difficult to crack according to experts on this... I did my homework with wireless networks, and most conjecture is still based on the old WEP protocol which is useless. WPA2 for a home or small office wi-fi is substantially adequate security.
There is no requirement to disconnect your wi-fi to secure your network, that is conspiracy nonsense.
Most routers today will allow you to specify IP's / MAC addresses of the machines allowed to connect, which is an additional security function you can use to stop your kids giving out the access to their mates and such, which is how issues can and do arise, or they begin plugging in all sorts of stuff using the wi-fi, that you don't know about.
If you want to go to a further extreme, you can use an additional cheap computer you have laying around as a RADIUS server and use WPA2 Enterprise, which acts as an authentication system to your wi-fi before a user can connect to it, being you must manually approve the user to access the system.
Giving wi-fi access is not giving access to your network either... as you should never leave your network group name as default for security purposes. This way, the network group name must be known to join it and access other computers / data storage devices.