Remove the spring.

Get a ball link end and drill a hole where the spring goes straight up into the rudder. Epoxy the ball link end in so that the hole is centered fore/aft.

Drill out the spring holder and solder in a piece of thin music wire, make it long enough to go through the ball link with enough extra so that it won't pop out when the rudder is fully deflected.

You now get very positive tail control (the spring is mush), but the music wire will asborb any energy without trasmitting it to the rudder if there's a problem.