I agree Gerald, they are similar to the twin rudders on “Double Trouble” and they also slipped as you know..
I will find something better before installing the deck but it will need to be double sided as I need a “push-pull” arrangement as the servo is now 320mm away from the rudder & I don’t want the control rods flexing. Also just realised that I need to fit a knurled knob to secure the servo arm so it can be removed without tools.
The arm needs to come off to remove the sail winch system.
It’s a work in progress & hopefully all bugs will be ironed out before the deck goes on.