Dog mess on chain (5)
I believe the answer is:
pooch
'dog' is the definition.
(pooch is a kind of dog)
'mess on chain' is the wordplay.
'mess' becomes 'poo' (I can't justify this - if you can you should give a lot more credence to this answer).
'on' is a charade indicator (letters next to each other).
'chain' becomes 'ch' (I've seen this in other clues).
'poo'+'ch'='POOCH'
Can you help me to learn more?
(Other definitions for pooch that I've seen before include "one of our best friends" , "Doggy" , "Dog (colloq.)" .)