Wellington Arch is in front of small fox (8)
I believe the answer is:
slyboots
'fox' is the definition.
(I know that fox can be written as slyboots)
'wellington arch is in front of small' is the wordplay.
'wellington' becomes 'boot' (Wellington boots are a type of shoe).
'arch' becomes 'sly' (I've seen this in other clues).
'is in front of' is a charade indicator (letters next to each other).
'small' becomes 's' (abbreviation - e.g. clothes size).
'boot' put after 'sly' is 'slyboot'.
'slyboot'+'s'='SLYBOOTS'
(Other definitions for slyboots that I've seen before include "wily type" , "cunning chap" , "One who's deep" .)