I would start with a good detailed map first, mark it up, and take it with you. better yet, take a GPS with a contour overlay then zero in on it with a depth finder. I really like areas where old creek beds intersect and areas where the old river channel curves close to the bank. You can also look for bumps and old stump beds as well. Large rocks and downed trees will not show on a detail map but can be gold if you can find them. A great way to locat them is to go to a body when they have it pulled down. That way you can find cover visually and mark it with a gps.