1. Make sure your walls are blast proof. If not, all it takes is one creeper to leave your base wide open.
2. Water is good for blast proofing, but make sure that your enemies can't climb the water up into your house.
3. Roofs are your friend. Without a roof, an enemy can easily ender pearl into your house or build a 1x1 tower and jump down.
4. Mines-make sure if you don't claim ALL of your mines to put a door blocking the entrance to the mine, or x-raying enemies will just dig down to your mine and enter your home that way.
5. Entrances-the less the better. I typically prefer no entrances, so the only way to get in is to tp in. If you do have an entrance, make sure it can't accidentally be left open.

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