Originally posted by Golden Corral:

How do you stop people from trolling the server? Just wondering if there is a way to stop the people doing this so other people who join the server can play too.

Should I build a fortress around the spawn? Or is this some sort of cheat?

You only play on private severs where you carefully vet everyone and white list through steam groups so they can't invite other people without approval.
Otherwise yes, people can use mods and cheats to grief servers and there is nothing you can do about it.