Regarding your inability to find a clear spot to GB - what may be happening (especially if you are searching for a "clean" spot using no discrimination (i.e., horseshoe mode)) is the detector is reacting to mineralization ground feedback as opposed to actual ground targets.  Try this next time you are having trouble finding "clean" ground to GB - use the pinpoint mode find a clear patch.  Pinpoint mode is a non-motion mode and is also not subject to reacting to ground mineralization.  If pinpoin