亡 wang2 亡
羊 yang2 羊
补 bu3 補
牢 lao2 牢
  1. lit. to mend the pen after sheep are lost (idiom)
  2. fig. to act belatedly
  3. better late than never
  4. to lock the stable door after the horse has bolted

Examples

亡羊补牢。

Info