For every one found inside wharf (4)
I believe the answer is:
pier
'wharf' is the definition.
(I've seen this in another clue)
'for every one found inside' is the wordplay.
'for every' becomes 'per' ('per' means 'for each' or 'for every').
'one' becomes 'i' (Roman numeral).
'found inside' means one lot of letters goes inside another.
'per' enclosing 'i' is 'PIER'.
(Other definitions for pier that I've seen before include "Support member" , "Landing stage; arch support" , "Breakwater; arch pillar" , "Break-water or landing stage" , "One jutting into sea" .)