If your control rod buzzes, find out why and make it stop. Buzzing rods will break in short order. Use the longest, stiffest tail blades that you can safely fit on your model. Remember the tail rotor puts a big load on the engine, in upwind maneuvers especially. When that happens, you can expect the tail to let go.
Power is good.
If during a descent, you notice the tail wagging, it's usually because the head is over speeding, causing the tail to turn faster. Fine-tune your throttle curve to prevent this.