Typically, concrete has a density of 150 pounds per cubic foot whereas steel is about 490 pounds per cubic foot. Water has the density of 62.4 pounds per cubic foot. So the buoyancy of concrete in water reduces its effective weight by almost half -- a much greater extent relative to the buoyancy effect on steel. (Underwater, concrete is about 87 pounds per cubic foot, whereas steel is about 427 pounds per cubic foot.)

So the 300 pounds (2 square feet) you are suggesting to Jud will actually weigh about 174 underwater. Unless it is also buried in some manner, that would hardly be an adequate anchor in even a local squall.