I take a razor saw and create a star pattern of grooves on the back of the prop. Get a cloth rag to hold the prop with when you tighten. I never try to take the prop on or off without a rag on the prop, and sometimes one on the wrench. Get the system snug, but where you predict another 1/4 turn or so to make it "really" tight. Turn the prop so on this last turn you have good leverage and angle between the end of the prop you are holding and the wrench handle. A small end wrench isn't going to do the trick. Get a long end wrench, use a towel so that you don't slip and slice your hand, use good angles to push the prop, and pull the wrench together on the final turn.

I just snug up the jam nut, not especially tight, but the mechanical stop is reached.

At some point it might still slip, then the sand paper is necessary as suggested above.
Thanks,
Jim