So ... slow work day? Every day?
Yes, although more than just defensive decisions. Basically everything about them. Gimping is DM metagaming. Instead of DMs worrying about players metagaming, reverse the dynamic. Get deep in to the non-performative part of roleplaying that NPC and structure the adventure however makes sense for that NPC's unique outlook without any concern for the players whatsoever, presuming the NPC had no fucking clue these PCs even existed before fantasy yesterday. Really think about what that NPC would do with its resources, location, personality and goals. And then stop. Don't worry about whether that's too easy or too hard. Ideally what you want is the location to be palpably that NPC's space, such that to overcome the space the players are metagaming the hell out of that NPC just to get to the last page, because unless they do there's no way to get a bead on "what they're supposed to do next".