ПРОЧНЫЙ _|_ LASTING / PROCHNYY [ˈprot͡ɕnɨɪ̯]
Hint with an alternative definition: it is a condition of a solid & strong object which has proof against changes (of a state), no patch is needed; it is like a pro-chained, prickly thing (it has many inner connections, and that’s why it is solid).
Hint with composition: no + approach — it is hard & solid enough to not let you in / challenge + broke, rupture = solid
Russian pro-tip: когда очень большой прок от вещи и нет порока; вещь исключительная — не прочая, её не выкинешь прочь, она прочно стоит
Mental visualization: strong construction (П, like a pillar, tower or gate) is under a hail of blows with a sledgehammer (Р), a wrecking-ball (О), an excavator (Ч), and next to it are fewer durable constructions (НЫ — pillars without a roof and foundation)