You can claim and therefore protect land on The Blame Train.
This allows you to prevent anyone else destorying or damaging your claimed land except those players you specifically allow.
You'll start with 200 blocks, but gain more while you play (100/per hour).
Here's a quick tutorial video. The same link will pop up in game if you ask for help claiming land.
(Sorry, embedding is disabled on this video)
There's also a full list of commands avaliable on the GriefPrevention wiki.
Don't have the tools? You can get a FREE golden shovel (and stick) once per day. Check out the Kits section on the main page.