unassailability

/ˌʌnəˌseɪləˈbɪləti/
noun
  1. The quality of being impossible to attack, question, or defeat.
    • Her argument's unassailability left no room for counterpoints in the debate.
    • The unassailability of the fortress made it a safe haven for the villagers.
    • The team's unassailability in the championship was due to their flawless defense.