Spot unwanted visitor in garden? (4)
I believe the answer is:
mole
I believe this clue is a double definition.
'spot' is the first definition.
(spot or blemish on the skin)
'unwanted visitor in garden?' is the second definition.
(a mole might dig tunnels in a garden)
(Other definitions for mole that I've seen before include "Underground worker!" , "Adrian ---, fancies Pandora; lurking spy" , "Burrowing mammal with velvety fur" , "Heap of soil (a 6 mountain?)" , "digger" .)