Alimony is like buying oats for a dead horse.

Alimony is like buying hay for a dead horse.

Paying alimony is like feeding hay to a dead horse

You've got to stop whipping a dead horse sometime.

Enough is enough. There is only so long you can beat a dead horse,

I'd call him a sadistic, hippophilic necrophile, but that would be beating a dead horse.