Where to secure barrier after last dog ate mail (8)
I believe the answer is:
gatepost
'where to secure barrier' is the definition.
Although both the answer and definition are singular nouns, I don't see how they can define each other.
'last dog ate mail' is the wordplay.
'last' suggests the final letters.
'mail' becomes 'post' (synonyms).
The final letter of 'dog' is 'g'.
'g'+'ate'+'post'='GATEPOST'
'after' acts as a link.
Can you help me to learn more?
(Other definitions for gatepost that I've seen before include "Side of an entrance" , "receiving confidences?" , "One privy to secret" , "Often a confidant" , "Upright beside a garden entrance" .)