I keep fiddling around with this idea.
I fiddled around with the LightSpeed 'Skeg/Rudder' idea.
There are no really good photos of it, but I can see where it could, with some work (and about ten prototypes) work out.
The retraction cable could pull it from an angle into the skeg box strait.
Perhaps there aren't any good photos because the rod hangs into water flow.

The drum is an OK idea, (google brings up several examples -- all for larger boats) but I quickly figured out that the rudder would have to be much farther astern, so it would stick up above the deck, or it would have to be too small.
As you point out, a drum rudder can't kick up if it snags. It'll break off, get damaged, or hang up.

I think the best idea along these lines so far seems to be the Epic 18 rudder-hull with retractable skeg.

It's interesting that all my fiddling seems to lead to it. (I haven't seen any unbiased reviews of it. I also haven't seen any grousing--so it must work)
So I guess I should quit screwing around and finish my Mystery project.

Another option that would require special materials would be a skeg that could be warped. Cables inside could contract. But I don't think a skeg is big enough to be an effective rudder.