A peg that shall not be moved
Figuratively: the matter is stable and there is no chance that it will collapse. Stable and secure.
("And at times you did not say to us thus (Did you not sometimes not say to us like this)?" He said to her: "It is a peg that shall not be moved" - Gittin 17a)
Translation
Expression (Hebrew)
יָתֵד הִיא שֶׁלֹּא תִּימּוֹט
Definition (Hebrew)
בְּהַשְׁאָלָה: הַדָּבָר יַצִּיב וְאֵין סִיכּוּי שֶׁיִּתְמוֹטֵט. יַצִּיב וּבָטוּחַ.
("וְהָא זִמְנִין לָא אֲמַרְתְּ לַן הָכִי (וַהֲלֹא לִפְעָמִים לֹא אָמַרְתָּ לָנוּ כָּךְ)? אָמַר לֵהּ: יָתֵד הִיא שֶׁלֹּא תִּמּוֹט"- גִּטִּין יז ע"א)