Border where dog loose (8)
I believe the answer is:
hedgerow
'border' is the definition.
(I've seen this before)
'where dog loose' is the wordplay.
'loose' is an anagram indicator (letters are loosened from their original positions).
'where'+'dog'='wheredog'
'wheredog' anagrammed gives 'HEDGEROW'.
(Other definitions for hedgerow that I've seen before include "Greenery between fields" , "Living boundary between fields" , "Growth around field" , "Bushy boundary" , "Field border" .)