OK, I've read all the responses and here is the straight dope.

Yes, wood props do compress and they are sensitive to humidity. But they are no more prone to being thrown than any plastic prop if checked for tightness. Once they have been installed for a long time, the tendency to loosen decreases. Of course if you break props very often (more than 2 or 3 over the life of the model), then they may not be for you.

A 4-way wrench is plenty for torquing down the prop. Even when I was a kid, with kid muscles, that was all it took.

Two cycle engines just don't throw props when adjust slightly lean, or even a lot lean. Four cycle engine do throw props when operated lean. While it is very easy to tell when a two cycle engine is lean by ear, four cycle engines really need to be set by a tach.

Throwing a prop or having the prop get loose on a two cycle engine is due to the engine back-firing while starting. This is caused by having too much fuel in the engine. It is so common to over-prime and then hit the engine with the starter. The inertia of the prop, starter, and spinner runs into the back-fire of the engine. This results in the prop getting loose or being thrown.

The proper proceedure is to prime the engine (usually by choking the intake and pulling over), then with the engine off of compression, hooking up the glow plug and pulling the engine over by hand through compression. If it is over-primed, you will feel a bump as the piston compresses the fuel/air mixture.

That bump is what causes the prop to come off when the starter is engaged.

Continue to pull the engine through the compression until the bump stops. At this point, most engines have a period of bump on one pull, no bump on the next. If starting with a chicken stick, pull it through the next bump, and flip the engine on the next. 90% of the time, it will start with one flip. If using an electric starter, use that after the bump. Remember, that until it is pulling through with a bump, then no bump, then it is still over-primed.

Once you start using this technique, you will have no more problems with throwing props. You can work on getting a good idle next.