Fine troubles with a heavy metal unlikely to miscarry (4-4)
I believe the answer is:
fail-safe
'unlikely to miscarry' is the definition.
I can't tell whether this definition defines the answer.
'fine troubles with a heavy metal' is the wordplay.
'fine' becomes 'f' (abbreviation).
'troubles' becomes 'ails' (as verb).
'with' is a charade indicator (letters next to each other).
'heavy metal' becomes 'Fe' (chemical symbol for iron).
'f'+'ails'+'a'+'fe'='FAIL-SAFE'
Can you help me to learn more?
(Other definitions for fail-safe that I've seen before include "Designed never to stop working" , "Unlikely to go wrong" , "Designed to prevent accidents in the case of malfunction" , "Device to ensure proper operation" , "Accident-proof" .)