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