How do you know your target is at 10” deep before you cut the plug? Does your detector indicate 10”, or did you discover the target was deeper than you thought after digging down that deep? On my Spectrum XLT, switching to pinpoint mode will give a display indication of depth in inches for a coin size target, but I’ve never seen a 10” depth readout.
If you got a strong signal for a target that deep, then it might not be a coin-size target, but something larger. If you got a whisper of a signal, I think the depth indication, if you even have one on your machine, might not be as accurate as for shallower targets. So I agree with several earlier replies; it all depends on where you’re digging.