How long are the 'limbs'? How deep is lake where you are planning to sink? Can you weight down the lower part and make the upper limbs a little shorter so that they will be below surface enough that boat traffic will not hit. Unless lake freezes solid you might have some of the limbs split from freeze but the death star should be below the depth that ice will form. These are just my thoughts. I know on Ky Lake several places where PVC is exposed all year round and does not show signs of damage.