Beer in can? That's a keeper (9)
I believe the answer is:
castellan
'that's a keeper' is the definition.
(thesaurus)
'beer in can?' is the wordplay.
'beer' becomes 'stella' (Stella Artois).
'in' is an insertion indicator.
'stella' going within 'can' is 'CASTELLAN'.
(Other definitions for castellan that I've seen before include "Governor of fort" , "Keep manager" , "Governor of a fortress" .)