Abstract: A dock support having a piling composed of an upstanding rod the lower end of which is adapted to be embedded in the bottom of a body of water and an external telescoping sleeve having a cap at its upper end which normally confronts and seats on the upper end of the rod. A passage exists between the confronting surfaces of the inner and outer telescoping members and such passage is occupied by air, rather than water. The air prevents water in the passage rising to the level at which it may freeze, but should water in the passage rise to the freezing level compressed air may be admitted to the passage via a valve under sufficient pressure to purge such water.