Simple and Cheap
Pete:
Drill a hole thru the portion of the latch lever that sticks outside of the fuselage when the latch is in the closed position. I use a light weight, brass padlock thru this hole. Body of the lock is covered with shrink tube to prevent "bruising" of the paint. Lock will stop honest people but is still easy enough to be cut by the bad guys should they wish to avoid breaking the canopy.
Terry, CFI
RV-9A N323TP