Superhero keeps duck for gondolier (7)
I believe the answer is:
boatman
'gondolier' is the definition.
(I've seen this in another clue)
'superhero keeps duck' is the wordplay.
'superhero' becomes 'Batman' (DC superhero).
'keeps' means one lot of letters goes inside another.
'duck' becomes 'o' (resembles zero - 'duck' in cricket).
'batman' enclosing 'o' is 'BOATMAN'.
'for' is the link.
(Other definitions for boatman that I've seen before include "Sailor" , "Water transport provider" , "One in charge of a small vessel" , "George - or Harris, maybe" , "Rower - bargee" .)