On another note: If the water at the edge of the base (if you terraformed it or build a wall around it) is still rather shallow, they will just stand there and smash through the terrain/walls and still do damage to anything built within that radius. Just keep it in mind, like if you build something at the outer edge of the island > might need repair after attack. If the island is big enough, maybe leave a radius around the actual base empty, functioning as a barrier.