A few years ago waterproof cameras were big, heavy and most of them needed additional plumb to stay under water.
But good old times changed and nowadays the waterproof cameras are small, lightweight, record movies in high definition but they sink in water.
O.k. modern things are not always bad, you get quite good pictures with these small wonders, but the sinking is a big annoyance.
Step 1: So lets built a buoy for it.
But not just a buoy, but a floating tray, on which the camera is served every time it is needed.
What you need is:
a small ring of styrofoam 17cm diameter (You can get this from your local hand craft shop, it is intended to be used to make a wreath)
some cloth 60 x 30 cm (I took organza, which is synthetic, light weight and open.)
some thread to sew it
a sewing pin or a sewing machine
an old shoelace