Discover a French fox's lair (7)
I believe the answer is:
unearth
'discover' is the definition.
(to unearth is to discover or find)
'a french fox's lair' is the wordplay.
'a french' becomes 'un' ('a' in French).
'fox's lair' becomes 'earth' (I've seen this before).
'un'+'earth'='UNEARTH'
(Other definitions for unearth that I've seen before include "Disconnect terminal" , "Bring out of obscurity" , "Expose" , "Cut a certain wire" , "Discover" .)