難攻不落：なんこうふらく [nan-kou-fu-raku]

攻めることが困難で、なかなか陥落しないこと。転じて、こちらがいくら働きかけても、相手がなかなか自分の要望を受け入れてくれないこと。

It is difficult to attack , that you do not quite fall . Turned , also lobbying much here is , that the opponent is not me quite accept their demands.