I am needing a gold detector and am wondering about ground balancing issues. I know that auto GB units are available but was wondering about the manual GB units like the older Fisher Gold bugs and Garretts Gold Scorpion. Do the manual units require constant, time consuming re-balancing as the soil changes? Do the auto GB units really keep up with the ground as it changes? I hope some of you with experience can help me decide. I prefer buying a used unit to save money. Thanks