Barrier that surrounds Slough church (5)
I believe the answer is:
fence
'barrier that surrounds' is the definition.
'fence' can be an answer for 'barrier' (fence is a kind of barrier). I'm not sure about the rest of the definition.
'slough church' is the wordplay.
'slough' becomes 'fen' (I've seen this in another clue).
'church' becomes 'ce' (abbreviation for Church of England).
'fen'+'ce'='FENCE'
Can you help me to learn more?
(Other definitions for fence that I've seen before include "Thief's dealer" , "With blade, fight" , "railings" , "Paling; criminal receiver" , "Barrier that serves to enclose an area" .)