He may not be able to repair/rebuild the walls, I sort of mentioned this earlier but it seems I didn't explain it well enough so here goes.
To build walls and towers, the parish village must have an adequately leveled architects guild. To level it, parish members have to donate goods to it. To actually build the walls, the parish needs to have stone, to get the stone parish members have to sell it to the parish stock exchange, and then the steward has to use parish tax money to purchase it for use in the castle. So as you can see, running a parish doesn't just fall on the stewards shoulders, but the members as well. If people don't have gold to pay the tax, no troops or resources for the castle. If people don't donate to the guilds, no access to defences or bonuses for the parish. If people don't sell resources(wood, stone, iron, and pitch), then no defences. No defences means the parish can't hold onto flags, and the steward needs flags to build guilds(including the architect's guild). Guilds grants access to troops and defences for the parish capitol and grants bonuses depending on the guild and level to all the member of the parish(Such as +x% wood production).
So in short, sell stone to your parish, always have some gold on hand to pay the tithe, and donate spare goods to the guilds regularly.
This is why I like this game, it has a lot of layers that you slowly get access to as you rank up. There's an actual political hierarchy, that leads to some good politics and diplomacy. Stewards are busy trying to get the most out of their parish, while the sheriffs above them are busy trying to get the most out of their stewards, and on it goes up to the king dealing with the whole country.