Minecraft wiki entry for Things_not_to_do, associated text: It is time-consuming to rebuild TNT traps. Instead, the player may want to use a more explosion-resistant material such as obsidian. Even using cobblestone helps, even if it is not fully explosion resistant. The player could instead use water to avoid terrain damage all together as water has the ability to absorb the destructive aspect of an explosion, but not the physics or health damage, which means that the target is still damaged and launched as normal.