Dictionary:

indefectible

  (ĭn'dĭ-fĕk'tə-bəl)

1. Having the ability to resist decay or failure; lasting.
2. Having no flaw or defect; perfect.

adjective

Supremely excellent in quality or nature: absolute, consummate, faultless, flawless, impeccable, perfect, unflawed. See good/bad.