I track my blades by taping the heli securely to the floor with packaging tape. I usually overdo the tape because I'd rather be safe than sorry. I keep a safe distance and would never attempt to hold it with the blades spinning!

Ground resonance? Yes, it exists and I have seen it - the first time when I was unaware of the issue, I throttled up slowly and the heli began to shake like crazy. I was quick enough to throttle back down as soon as it started, and nothing was damaged. However, I have since learned that is is very easy to avoid;

Throttle up slowly to the point where the rotor just starts spinning. Let the blades "catch up" to that throttle speed, and once they do, throttle up quickly to about 50% so that you get past the resonating frequency. If everything is balanced reasonably well, all you get is a slight vibration for a split second as the rotor accelerates through that sweet spot and then it's gone completely. From there you can accelerate slowly again until you've got sufficient positive pitch to check the tracking.

***If the heli begins to shake violently before you get past the resonating frequency, throttle back down quickly - do NOT attempt to accelerate through it!!! You either throttled up too slowly, or maybe your setup just isn't capable of accelerating fast enough...?