Minnow time, the Key is having a Quality depth finder with a gps to follow the contour lines as CC mentions below. also You can record a trail that will dislay on your map to help you know what area you have covered, allowing you be sure you covered an area thouroughly. Technology isn't all that expensive any more, and you can sometimes find a good used unit as people upgrade. the fuel saved alone will make up for the cost of the unit... Good luck ..