Turn Wifi Off via command line
You could use this to turn it off:

sudo ifconfig en1 down


And if you want to get it back up, just type up, instead of down

Just make sure that en1 is the right interface or you can easily kill off your ssh access :)

P.S. As Lri noted in the comments below, you can quickly disable the correct network interface with just 1 line:

sudo ifconfig `networksetup -listallhardwareports | grep -E '(Wi-Fi|AirPort)' -A 1 | grep -o "en."` down


This will detect the correct Airport/wireless device and will turn it off