Dog pen Erica locks unhappily (6,7)
I believe the answer is:
cocker spaniel
'dog' is the definition.
(cocker spaniel is a kind of dog)
'pen erica locks unhappily' is the wordplay.
'unhappily' indicates anagramming the letters.
'pen'+'erica'+'locks'='penericalocks'
'penericalocks' with letters rearranged gives 'COCKER SPANIEL'.
(Other definitions for cocker spaniel that I've seen before include "Breed of small dog" , "Breed of gun dog" , "Small dog used in game shooting" , "Ponies crackle (anag) - dog" , "Mutt" .)