The "Further Seed Customisation" patch (https://hub.spigotmc.org/stash/projects/SPIGOT/repos/spigot/browse/CraftBukkit-Patches/0107-Further-Seed-Customisation.patch) provides necessary tools for server operators to prevent the discovery of their world seeds via the weakness of the pRNG used to position villages and scattered features (temples, huts, igloos).

However, Ocean Monuments and Slime spawning chunks suffer from exactly the same weakness; both have their own hard-coded seed values (10387313 and 987234911, respectively) which should also be made configurable. Woodland Mansions and Nether Fortresses do not require this protection because their structure generation rules make it impossible to identify the specific chunk in which the structure spawning began.