One thing I use to do that really allowed me to learn my beaches- there were times when I just carried my scoop and a long thin diameter, but strong, metal probe. With just these two things I'd take hikes up and down the beach when it was flat and every so often I'd see how deep I could sink the probe without too much effort. Most often I had no trouble sinking the probe a lot further then I could detect but every once in a while I'd hit "an area" where it was much harder to sink the probe. From here I'd keep repeating the process to get an idea just how large this firmer/denser area was. I'd use my scoop to see what was making it denser, most often it was shell-pack or just really hard, tightly packed, "gray" sand, but it was firmer, denser bottom, the type of firm that could support those heavier items I wanted to find. I even mapped these areas for future reference and it eventually paid off and still does from time to time.