Behind, as with the rent, maybe (6)
I believe the answer is:
astern
'behind' is the definition.
(at the back or behind of a ship)
'as with the rent maybe' is the wordplay.
'with' says to put letters next to each other.
'maybe' indicates an anagram.
'rent' is an anagram of 'tern'.
'as'+'tern'='ASTERN'
(Other definitions for astern that I've seen before include "Towards a ship's rear" , "Abaft" , "Behind (naut.)" , "Towards rear of a vessel" , "Toward the back of a boat" .)