For technical reasons, you need to know the seed of your world to use Ocean Monument Finder, unless, of course, you want to find a seed for a new world. If you're playing SSP, the app is able to fetch the seed from your savegame. Alternatively, you can use the /seed command in...
Hostile Mob should not spawn inside Ocean Monument.. This is a direct quote from the Official Minecraft Wiki 'Guardians are the only hostile mobs able to spawn within the 58×58×23 area containing the monument; normal Overworld hostile mobs will not spawn inside.' The fact that hostile mob...