What you propose would certainly work, but may be way more that actually needed.
Here's a photo of some nice rudders hanging on a new boat.
You will notice that they cover better than half of the prop blast.
They are mounted low.
I don't think they are in any real peril from any thing.
This boat is being rigged by folks who know what they are doing.
Just remember that the higher they are mounted, it make the path for the forces generated longer through the rigging, so it can be applied to the hull.
These forces could be substantial if the boat was stuck.
I have seen prop guards visably twisting under these forces.
Makes me run for cover!
Here's a picture of Jdotson's boat with triple rudders.
He seems more than happy with how it works.
I would envite you to study the pictures in the gallerys here, and decide what you think is best for your airboating.
Also,
Many believe that one big rudder is a thing of the past.
A relic from times gone by. Perhaps that's what I am too.
We have boats with dual rudders also.
They run great.
Just take your time, and make sure your rudders are rigged well.
There's alot riding on it.
Later