A method and apparatuses for verifying Cryptographically Generated Address signature are provided. A releasably lockable latch is mounted or mountable on the first end of the flexible member for locking the first end of the flexible member to a corresponding first exterior wall of the spa. The inverter outputs a driving voltage that is based on a driving voltage reference superposed with the superposed voltage reference to the electric motor. The frontal area encompassed by one of the skeletal frame members is less than the frontal area encompassed by the other skeletal frame member, and the two skeletal frame members are substantially overlappingly disposed with respect to each other so that the respective netlike coverings form higher point and a lower point goal zones. The bottom of the trench reaches at least the inside of the substrate.