How did you "cut it off"? Assume it is on a taper and keyway so I hope you have not cut anything off the shaft. The normal way of ensuring the prop does not come off is first to make sure that it is machined to the correct taper, slide it on the shaft until it bottoms on the taper and then put a lock nut on. Easiest way of ensure the lock nut does not come off is to use a castellated nut and drill the shaft for a locking split pin. Alternatives are to use a lock washer with one ear bent to the prop and the other to the nut, or drill and tap to take a socket headed grubscrew. You may find that you don't need a cone anode with a fixed prop if you have a hull anode close, or a shaft anode is easier to fit.