Here the illustration of what I had in mind: scimitar blades from modern submarines. You will notice that to bring the safety aspect, the winglets must be bent towards the opposite side of prop rotation direction.
In fact rotating winglets during rotation create a solid ring. Of course, the blade extremity must not be sharp and dangerous like scimitars. They coul be thickened like an olive.
Applied to @foiledagain 156mm prop, this is in yellow what it would look like adding a tiny appendix to smooth the edge: