During LOCH, Peach Blossom Island was the unviolable domain of East Heretic Wong Yerk See. Unwelcome intruders dared not set foot on Peach Blossom Island, lest they fall prey to the wrath of Wong Yerk See. Even if they didn't come face to face with the Lord of Peach Blossom Island himself, and didn't need to face his martial arts, intruders could not penetrate its many traps and mazes. That's why even Greats such as North Beggar Hung 7 Gung, West Poison Au Yeung Fung, and Chow Bak Tung tread on Peach Blossom Island with caution.
Wong Yung always believed that should the Central Plains fall under Juchen or Mongol control, she and her loved ones might have a safe haven on Peach Blossom Island. How strong a sanctuary would it be against a Juchen or Mongol siege, however? In the long run, the Juchen/Mongol army will definitely overrun the island (sheer attrition guarantees that), but how much time, manpower, and resources will the Juchen/Mongols need to expend to take Peach Blossom Island? If you were a Juchen or Mongol general, would you consider the island a worthwhile target (assuming that your spies have confirmed that anti-Juchen/Mongol wulin forces are using the island as a base for guerilla war against the Juchen/ Mongol regime)?