Dog with ratty coat is mine (8)
I believe the answer is:
colliery
'is mine' is the definition.
(thesaurus)
'dog with ratty coat' is the wordplay.
'dog' becomes 'collie' (collie is a kind of dog**).
'with' is a charade indicator (letters next to each other).
'coat' suggests removing the centre.
'ratty' with its middle taken out is 'ry'.
'collie'+'ry'='COLLIERY'
(Other definitions for colliery that I've seen before include "Mining complex" , "Coal-mining establishment" , "Coal mine" , "Where a coalminer goes to work" , "Pit" .)