When dogs go to earth, it means trouble (5)
I believe the answer is:
curse
'trouble' is the definition.
(curse is a kind of trouble)
'when dogs go to earth' is the wordplay.
I cannot really see how this works, but
'dogs' could be 'curs' (cur can mean a violent dog) and 'curs' is located in the answer.
'earth' could be 'e' and 'e' is found in the answer.
No letters remain.
This may be the basis of the clue (or it may be nonsense).
'it means' is the link.
Can you help me to learn more?
(Other definitions for curse that I've seen before include "Imprecation or oath" , "Imprecate" , "Execration" , "It's bad spelling" , "Utter obscenities" .)