'Sonner l'hallali' is a French expression that means to announce your victory over (or your defeat of) someone or something. In its strictest sense it is the name of the call on the hunting horn when the prey is put to death. Like many of these sorts of terms, it is a contraction -- in this case of 'halez à lui !' (set after him! i.e. a cry ordering the dogs to go after the prey) and was originally used at the beginning of the hunt, not the end.
Its opposite is 'boire le calice jusqu'à la lie' (to drink the chalice to the dregs i.e. to suffer complete humiliation). As one of my 'learn-a-French-phrase-a-day' websites points out, there is a rather neat play on words going on here.