Small man had erection in the garden (4)
I believe the answer is:
shed
'erection in the garden' is the definition.
'small man had' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'man' becomes 'he' (pronoun for a man).
'had' becomes 'd' (I've seen this in other clues).
's'+'he'+'d'='SHED'
(Other definitions for shed that I've seen before include "dropped" , "Garden store" , "Lose as trees do leaves" , "Drop - cast off" , "Abandoned" .)