Dan,
One of the things I have learned from experience of digging too many nails and other trash is to go over the target to get the nice tone, then move the coil back while going side to side to find the start of the signal. Now that I know where it starts I will look at that spot and come at it at a differnt angle to see if it is still gives a signal in the same area. I may go all around it sometimes and maybe just 2 or 3 differnt angles as if it is only one way and nulls the other chance are it is a iron false, but doing this I have also pinpointed it too if it was a good signal, but will go to pinpoint too to make sure of the pinpoint. Now several times on the real iffy ones I will after I check it in the reg hunt mode, then pinpoint and recheck the signal after I have pinpointed too. If it is still iffy I will dig, but if it has proven to me the signal is moving and it is a false I will walk away.
Rick