足が出る

[ashi-ga-deru]:

Literal translation:

legs stick out

Meaning:

(1) go over budget

(2) reveal secrets mistakenly

Examples:

彼らは旅行で爆買いして足が出た。:

They went over their budget on a shopping spree during their travel.

彼女はしゃべり過ぎて足が出た。:

She talked too much, letting her secrets slip.