Tools exist that can work out your world seed from things like ore positions or structure locations. A known seed lets cheaters find bases, loot and structures. These steps make it harder on Paper and Spigot servers.

Shift structure positions

1. Open spigot.yml in the Files tab.
2. In the seed- section for structures, change a few of the numbers. Changing one is enough. This moves villages, temples and other structures away from where the real seed would place them.

Turn on Anti-Xray engine 2

Follow Enable Anti-Xray and set engine-mode to 2. The fake ore blocks also confuse seed-cracking tools.

Finish

Save your files and restart the server. Structures in chunks that are already generated will not move, so this works best on new or fresh worlds. See Change Your World Seed if you want to start over.