So a thought I had - do you need the "+3 Walls always remain unscathed" sentence? Having it be a Sentence seems to invite players to engage with the walls, but it being +3 and how broad it is seem like it's discouraging to the attempt. If you want players/characters to be more creative about how they get into vaults, maybe something like "+0 Bastille always denies easy access."? They'd still have to put at least +1 effort into it, and then you get the fun of Realizing the sentence once they've had some wins to make it difficult again.