One method I've seen used on some aircraft is to use a stick-mounted
normally open trigger-switch (or push-button if your stick can't accommodate
a trigger-switch) wired in series with the power to the system that needs
protection (in this case, the trim system). To operate the trim, the
in-line, or safety switch must be depressed before the desired trim servo
can be energized with it's individual switch. Should a servo start to run
away, you'll notice it the instant the safety switch is depressed and you
can stop it merely by releasing the switch. If you have breakers for each
servo, the safety switch can either be a three-pole unit or it can be
inserted ahead of the breakers in a common power line.

With this method, the breakers can be pulled and the offending system
isolated at the pilot's leisure.

For the guys that had their trim switches stick, the chance of both switches
failing at the same time and in the same manner is miniscule.

Dan Schaefer