Aha, I was picturing the sort of buoy that you use to mark crab traps.
xort - the difference between poly line and the buoy is probably one of visibility. Waters in PNW are pretty murky and vis is basically zero below ten feet, especially during summer when that pesky environment thing starts growing all over the place.
One thing I would do with the little buoy -- or with the poly line -- is to somehow paint it with reflective paint or otherwise make it reflective. Even on low-vis days, reflective objects can stand out like spotlights underwater.
1972 Catalina 27