Oh, here's a pretty good method for keeping people off your network EVEN IF they manage to get your wifi password, turn off dhcp, set up a custom netmask (anything non-standard or just move a little away from the defaults*) and just set up your ip addresses and dns servers manually. They'll have a lot of fun trying to figure out your setup if they figure out why it's not working automatically
*instead of 192.168.0.1 / 255.255.255.0
you could just use a different subnet.. e.g. 192.168.12.1 or something along those lines..
If you're technically inclined, set up a custom mask entirely.