Senior Single Tennis Training Base And Tennis Ball SeatStore Description: Fill the base with water and it instantly becomes heavy enough to hold the unit in place. Non skid pads underneath help keep it stable. Unwrap the cord, hit the ball as hard as you want, and the ball bounces back to you. The harder you hit the faster the ball is rebounded to you. Rubber cord is 15 feet long and stretches to 30 feet for hard hit balls. To shorten the rebound, wrap some of the cord around the base to your desired