to remember a benefactor or an act of kindness for as long as one lives

您的救命之恩，我必将铭心镂骨，永志不忘。

idiom · deeply and permanently impressed; engraved in one's heart and carved in one's bones

那段艰苦的岁月让他铭心镂骨，时刻提醒他要珍惜现在。