As I recall, Saint George killed a dragon that was living near a pool of water that was a water source for a city and thereby extorting maidens as food from the locals, but in the case of the St. George & Dragon story, I’m not clear on if the dragon was ‘guarding’ the water or just happened to be living near it and the locals were tossing it maidens because the dragon demanded them or just to distract it long enough to fill a couple of buckets. I guess if it was a town in the desert, water could be seen as a treasure, but I’m not quite ready to give players XP every time they fill up their water skins. It’s been years since I read the St. George story, but I don’t recall getting the impression that the dragon in it was particularly ‘human’ in it’s thinking (unlike Smaug).
Are there other ‘dragons guarding treasure’ that I am just not thinking of? I know dragons are quite popular in Asian folklore, but I don’t know much about the folklore of the far east and how dragons behave in the old stories from Japan, China, etc.