Cover entrance to lock? (5)
I believe the answer is:
apron
'cover' is the definition.
(I have seen 'Protective cover ' mean 'apron' so perhaps 'cover' could also mean 'apron')
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for apron that I've seen before include "Cook's protector" , "Cook's garment" , "Area for aircraft not in use" , "area in front of aircraft hangar" , "Pinny -part of the fairway leading onto the green" .)