The collar includes a buoyant forward section and a controllably buoyant rearward section pivotally connected to {HEAD ~ the rearward section} for {TAIL ~ pivotal movement} between a horizontal floating position and a sunken position 
The collar includes a buoyant forward section and a controllably buoyant rearward section pivotally connected to { HEAD ~ the rearward section } for { TAIL ~ pivotal movement } between a horizontal floating position and a sunken position
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH