亡羊补牢

วัวหายล้อมคอก; แก้ไขแม้ล่าช้า; สายแต่ยังดีกว่าไม่ทำ

lit. to mend the pen after sheep are lost (idiom); fig. to act belatedly; better late than never; to lock the stable door after the horse has bolted