nothing is fool proof.....but provided you have a robust throttle linkage(ball link to ball link) with no binding and you have strong arms on both sides, everything mounted securely you can suffice with that......thats the way i have been doing it lately...

however when i first started out i wanted every last bit of RPM and i would throw the servo into "overload" and cause it to bind, thus killing the servo prematurely...when in reality no performance (rpmwise) is gained after the throttle flap/valve/plate is opened past 80%.... now i adjsust my throttle servo accordingly and i get a more linear response, where i can differentiate between half throttle 3/4 throttle and full throttle,,,,, where before i really couldnt

one time i had a thin 1/16th pice of aluminum i salvaged from a custom computer case...the throttle arm i made "cracked" due to fatigue, thank God i had a choke servo..... rather than flying till i ran out of gas i choked it at the right momen and landed safely....... another time when i was young and dumb i didnt secure the throttle arm servo screw(i also removed the throttle return spring, a BIG NO NO), and had to rely on a 42% ignition kill activated by a vacant channel... it worked... ive also had an experience with a previous 42% ign kill that caused my engine to run erratic....once removed the engine ran as expected..... ive also had a throttle servo dismount yielding a truely unexpected dead stick, thankfully i took my plane home unharmed

summary... if your thottle servo is of higher quality, and have zero binding(can be confirmed with http://hangar-9.com/Products/Default.aspx?ProdID=HAN172) and the servo mounted to a servo box, and the box is glued and screwed you have a lower chance of having to rely on a secondary backup to kill your engine..... if you want it all do the previous ,plus install a choke servo, and an opto ign kill, and have 3way security