Stock held by private landlord (9)
I believe the answer is:
innkeeper
'landlord' is the definition.
(I've seen this before)
'stock held by private' is the wordplay.
'stock' becomes 'keep' (I've seen this before).
'held by' means one lot of letters goes inside another.
'private' becomes 'inner' (as in one's private or inner thoughts).
'keep' put within 'inner' is 'INNKEEPER'.
(Other definitions for innkeeper that I've seen before include "Manager who made extra provision for visitors" , "Publican" , "Mine host" , "For example, Mistress Quickly" , "Pub runner" .)