鉄てっ壁ぺき

noun

iron wall; impregnable fortress

Literal or figurative strong defensive barrier; often used in military, sports, or security contexts.

• 敵てきの鉄てっ壁ぺきの守まもりを破やぶるのは難むずかしい。

  It is difficult to break through the enemy's iron wall of defense.

• 彼かれのガードは鉄てっ壁ぺきだ。

  His guard is an impregnable fortress.

noun which may take the genitive case particle 'no'

impregnable; invulnerable; unassailable

Adjectival use with の, describing something extremely solid, unbreakable, or impossible to defeat.

• 鉄てっ壁ぺきの防ぼう御ぎょを誇ほこるチームだ。

  It's a team that boasts an impregnable defense.

• その計けい画かくは鉄てっ壁ぺきのアリバイがあった。

  The plan had a cast-iron alibi.