Dogs at large he let loose in violent dispute (2,11)
I believe the answer is:
at loggerheads
'in violent dispute' is the definition.
(I've seen this before)
'dogs at large he let loose' is the wordplay.
'let loose' indicates anagramming the letters.
'dogs'+'at'+'large'+'he'='dogsatlargehe'
'dogsatlargehe' is an anagram of 'AT LOGGERHEADS'.
(Other definitions for at loggerheads that I've seen before include "Disagreeing with" , "In violent disagreement" , "In violent dispute" , "Quarrelling" , "In confrontation" .)