Duck a risk here: fish unlikely to stay frozen long? (5,2,4,3)
I believe the answer is:
skate on thin ice
'duck a risk here' is the definition.
(to skate on thin ice is to take a risk)
'fish unlikely to stay frozen long?' is the wordplay.
'fish' becomes 'skate' (skate is a kind of fish).
'unlikely to stay frozen long?' becomes 'onthinice' (thin ice will melt quickly).
'skate'+'onthinice'='SKATE ON THIN ICE'
(Other definitions for skate on thin ice that I've seen before include "feeble attempt to keep fish fresh?" , "ducking the likely outcome?" , "fish displayed thus might not stay fresh for long" , "Take risks" , "Court trouble" .)