Gun dog detailed to fetch (8)
I believe the answer is:
retrieve
'fetch' is the definition.
(retrieving is a kind of fetching)
'gun dog detailed' is the wordplay.
'gun dog' becomes 'retriever' (retriever is a kind of gun dog).
'detailed' means to remove the last letter (the word must be end-less or 'de-tailed').
'retriever' with its final letter taken away is 'RETRIEVE'.
'to' is the link.
(Other definitions for retrieve that I've seen before include "Revere it to get back" , "(Of dog) fetch shot game" , "Find and bring back" , "Search for and discover" , "Get back or fetch" .)