Hole on cover for pool (4)
I believe the answer is:
lido
'pool' is the definition.
(I've seen this before)
'hole on cover' is the wordplay.
'hole' becomes 'O' (O looks like a hole).
'on' means one lot of letters go next to another.
'cover' becomes 'lid' (lid is a kind of cover).
'o' put after 'lid' is 'LIDO'.
'for' is the link.
(Other definitions for lido that I've seen before include "Idol (anag.)" , "Open-air swimming pool" , "Public bathing beach" , "Venice's beach island facing the Adriatic" , "Public open swimming pool" .)