Wary of fish counter with rusty edges (5)
I believe the answer is:
leery
'wary' is the definition.
(leery can mean wary or cautious)
'fish counter with rusty edges' is the wordplay.
'fish' becomes 'eel' (eel is a type of fish).
'counter' says the letters should be written backwards (counter can mean in the opposite direction).
'with' is a charade indicator (letters next to each other).
'edges' means to remove the middle letters (I've seen 'edges of' mean this).
'rusty' with its middle removed is 'ry'.
'eel' in reverse letter order is 'lee'.
'lee'+'ry'='LEERY'
'of' acts as a link.
(Other definitions for leery that I've seen before include "Knowing" , "Shy" , "Sly, cunning" , "Cunning - wary" , "In slang, wary or suspicious - reely!" .)