Put one's foot down:

把腳放下 ×

下定決心 √

例句：

I shall have to put my foot down and stop this nonsense.  

我必須采取堅定的態(tài)度，制止這一荒謬的事情。

Keep one's feet on the ground:

腳踏實地 √

例句：

Keep your eyes on the stars, and your feet on the ground.

目光高遠(yuǎn)，腳踏實地。

Stand on one's own feet:

用自己的腳站著 ×

自力更生 √

例句：

I hope you can stand on your own feet.

我希望你能夠獨立自主。