usually tail feathers and wings break under enormous "G" forces generated during flight. Sometimes it is a simple joint failure, but most of the time it's because of forces that can only be caused during flight. When I'm just warming my engine up, I stand with the fuse between my legs, and the horizontal stab at my ankles/calfs. If I'm tuning an engine, then I get on one knee, on the side of the needle valve, lay my radio on the ground where it is accessible, hold the plane by the fuse, on top, just in front of the wing. then, I run the engine up to full throttle, adjust the needle, and bring it back down. So far this has proven failry safe. There is no real fool-proof way to do it, you just have to pick the safest way, the way you feel most comfortable with, and be VERY careful. Do not allow anyone to be in front of, or to the side of the prop, and do not let anyone be in front of a wing for that matter. If the plane gets loose at full throttle, and the wing hits someone on the leg, then the plane is likely to spin around and bite them. SAFETY, SAFETY, SAFETY.!!!!