Prison found in southern Irish land (4)
I believe the answer is:
stir
'prison' is the definition.
(informal term for prison)
'in southern irish land' is the wordplay.
'in' means one lot of letters goes inside another.
'southern' becomes 's' (abbreviation).
'irish' becomes 'IR' (abbreviation for Irish).
'land' becomes 't' (I can't justify this - if you can you should believe this answer much more).
's'+'ir'='sir'
'sir' enclosing 't' is 'STIR'.
'found' acts as a link.
Can you help me to learn more?
(Other definitions for stir that I've seen before include "fuss" , "jail" , "Prison (slang) - disturbance" , "Awaken" , "beat" .)