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