As said above ..armband or line of polystyrene on handle...(which you could paint black etc)...which will flip it make it more visible and be a small sail...also as said above v v v occasionally in big waves no upwinding will get it back...especially in eight metre plus deep green mucky vis where a great white might be hanging out!!
..have seen some pple who use a leash anyway despite the bouncing back hit the head type situation..mostly though only because of fear of loosing board in grt,white territory thats their reason
97% of the time except rare large waves far out to sea conditions it can be retreaved by good tight LONG 50m one arm as a rudder bodyD as said above also.good luck..
Also..if u loose sight of the board if u havent allready do a jump to.try and see it but I guess u allready thought of that