Quote Originally Posted by NightwindKing View Post
I've got a Metsuke in each of my 'problem provinces', and still end up with this issue.
Try sending a ninja in to take a look around. Ninja and metsuke are strong against different agent types, and so what's overlooked by one might be noticed by another. Assuming that there is something to find, of course.

One of them, I think Buzen, is 100% Christian, and I'm a Shinto/Buddhist clan. I have a fully upgraded temple complex AND a monk, and the religion hasn't changed at all. What gives? Is it because of the Nanban trade port? I'd happily destroy it, as I dont need/use it, but I'd be afraid I couldn't build another one later if I needed to.
That kind of religious difference is very bad! It's almost certainly the cause of most of your problems. Put your mouse cursor over the up/down arrow icons next to the religious summary on the province information screen. That will break down exactly what is affecting each religion. Act to remove anything which gives a positive factor to Christianity.

The Nanban port spreads Christianity; if its spread % is higher than that of your temple, it will prevent the temple from converting the population. Even if it gives a lower percentage than your temples, it will hamper your efforts. Burn that port down and you should start to see a difference. It is possible to keep one and have your population remain happily Buddhist; since you are already having difficulties it would be best to try that out another time, when you have had more practice at keeping the peasants happy. If you destroy the Nanban port you will be able to make a new one later, provided you have had the event which offers the chance to trade with the foreigners. All of the clans get that at different points in the campaign; it moves from the west side of the map to the east, so clans on the west side get it earlier.

Monks work best in groups of 2-3 unless they are level 5 or 6. Low level monks don't have a very high conversion ability, so stacking the bonuses provided by multiple monks is the best way to get a big jump in the percentage. Especially when combined with Buddhist buildings.

Check the neighbouring provinces for Christian buildings. Some of them spread the religion to all provinces which share a border. It could be that your enemy has one of these buildings, and is still converting your populace without actively doing anything. If you find one of these buildings get a ninja to sabotage it. That will temporarily remove the bonus. Repeatedly sabotage it until you can safely capture the province which contains it.

Check for enemy missionaries in your province. They do not need to be on a mission to convert the population, their mere presence is enough.