There is an old underwater railroad track on Jordan lake and we found a section ten feet deep. We spent a couple of hours going back and forth over the RR bed writing down different speeds and different jig combinations. Our favorite combination was a two jig rig with a 1/16 and a 1/32 pulled at .8. We would keep going over the RR until the rod tips started bouncing and we knew we had hit the bottom. Write that down and then try another combination. Takes some time, but you develop patterns and confidence you are fishing the right depth.