To claim a plot of land, you need to place a Land Claim Kit. Once placed, you can disable and enable building within a 30-meter radius via a switch on the Base Flag Pole. Its purpose is to stop any players from building on your plot of land. The Base Flag Pole is not bound to your character or base. Make sure you secure it. Base Flag Poles can currently be destroyed with a sledgehammer or hacksaw. They cannot be moved once placed. You can add as many as you can afford/find if you want a larger base.
You can craft a Basic Flag to attach to your Base Flag Pole using a knife and rag. When the Base Flag Pole is switched to Construction Disabled, it restricts all players from placing any object within the radius of the pole. So when you are not at your base, keep Construction Disabled so players cannot build into your base and or boost with barrels etc. The Base Flag Pole will default back to Construction Disabled after every server restart as an extra safety precaution.