Rocky island in southern Irish county (6)
I believe the answer is:
'rocky island' is the definition.
(I've seen this before)
'southern irish county' is the wordplay.
'southern' becomes 's' (abbreviation).
'irish county' becomes 'kerry' (I've seen this before).
'in' is the link.
(Other definitions for skerry that I've seen before include "tiny island" , "small island" , "Rocky island or reef" .)