I also agree with everyone that the tapered bub with a key slot is by far a very good way to attach.
Also you can order bolts with holes drilled sideways in bolt heads and after you have tightened and loctited etc. you run a good strong wire between the bolts so there is no way possible for them rotate and loosen themselves.
Or if you want a 100% sure way to retain the prop. You buid a new shaft with a step in it leaving extra length to be turned down  smaller and threaded and then add double locking nuts with a  a provison in shaft for a keyed locking tab to be installed between the nuts and after they are tightened you bend over the retaining tabs in opposite directions so both nuts are captivated.
Only way this can open is if you break the shaft or bend back the tabs and loosen the jam nuts. This is how heavy trucks secure axle bearing hubs which are subjected to huge load pressures and also are reversed which make it even more difficult to retain.