Hi Lisa In UK the phrase is normally "flogging a dead horse", which means that however hard you try a situation will not improve, so you are wasting your time and effort. This comes from the idea that you can work a horse until it collapses and dies from exhaustion - after that it is not going to work any more!

Flogging a dead horse", (alternatively "beating a dead horse") is an idiom that means a particular request or line of conversation is already foreclosed or otherwise resolved, and any attempt to continue it is futile. The first recorded use of the expression with its modern meaning is by British politician and orator John Bright, referring to the Reform Bill of 1867, which called for more democratic representation in Parliament, and about which Parliament was singularly apathetic. Trying to rouse Parliament from its apathy on the issue, he said in a speech, would be like trying to flog a dead horse to make it pull a load. The Oxford English Dictionary cites The Globe, 1872, as the earliest verifiable use of flogging a dead horse.