(draw) a line in the sand
US /drɔ ə laɪn ɪn ðə sænd/
UK /drɔ ə laɪn ɪn ðə sænd/

1.
劃清界限, 設定底線
to establish a limit beyond which one will not go; to set a boundary or a point of no return
:
•
The company decided to draw a line in the sand regarding employee benefits, stating no further concessions would be made.
公司決定在員工福利方面劃清界限,聲明不再做出任何讓步。
•
I told him he could borrow my car, but I drew a line in the sand at him taking it out of state.
我告訴他可以借我的車,但我劃清了界限,不能開出州外。