ehm... couple it with the squats AND the flaps perhaps?
GND+flaps 0 -> radar off
GND+flaps whatever -> radar useable
FLT+ flaps 0 -> radar useable
No takeoff without flaps and after landing you anyway select them up!
SHOW ME THE MONEY!
(maybe it can buy me a course in learning to write proper English, so I don't have to edit for typo's the whole time
)