Destruction for reperfusion in medical diagnostic ultrasound is synchronized to motion. While such retractable devices are bolted or otherwise securely fastened to the vehicle, the retractable devices are susceptible to being damaged or torn off of the vehicle due to air movement such as headwinds, wind gusts, and turbulence from passing vehicles. Thus, the slack portion is expanded and deployed toward a windshield earlier to form \u201ca wall\u201d. The locking device has a pair of clamp arms that are resiliently biased together but that are deflected apart by a separator until the arm shoulders snap behind the stationary shoulders.