Well, I suppose Gensōkyō's barrier can be equated to a wall, with Yukari being the one taking care of it. I do like to think that it's not just her who patches up any hole that might come up. It is probably a collective responsibility among the sages who have access to the barrier.
Or maybe it is under the sole purview of just the Hakurei God? While Reimu is the zookeeper of the Human Village, it's the Hakurei God that takes care of the barrier? 🤔
