... pay for a dead horse花冤枉钱 mount on a dead horse [口]重提早已解决了... flog a dead horse 徒劳无益 ...
双语例句
1
The guard replied calmly: "Your Majesty, this is to let the general public know that Your Majesty is willing to paya high price for even a dead thousand-li horse, let alone a live one."