Gardener about to retreat at back of house (4)
I believe the answer is:
hoer
'gardener' is the definition.
(I've seen this before)
'about to retreat at back of house' is the wordplay.
'about to' becomes 're' (I've seen this in other clues).
'retreat' is a reversal indicator.
'at back of' is a charade indicator (letters next to each other).
'house' becomes 'ho' (abbreviation for house).
're' backwards is 'er'.
'er' after 'ho' is 'HOER'.
(Other definitions for hoer that I've seen before include "I tidy the garden" , "User of a gardening tool" , "Weeder" , "Gardener" , "I weed" .)