Observation. I look at the surfline and other beach cams. Hopefully there is a jetty or a wooden post to objectively look at. You can then observe when more or less rocks are showing. Other clues when you find yourself at an unfamiliar beach swinging your detector are:
soft sand in the water. Your feet are sinking in. Good hard packed sand should be slightly softer than concrete under your feet without much give. Your footprints should be really shallow.
Rocks and heavy objects on top. If there are no rocks coral or shells on top of the sand, it may be sanded in.
A lack of heavy targets. When you are pulling light aluminum, bottle caps and pull tabs from a foot down go grab a beer or at least turn off the detector to save batteries, you are sanded in.
East coast. If you are on the east coast, you are sanded in. Joking. Conditions vary by location. Sometimes just walking a quarter of a mile can make all the difference. If the beach is a limitless expanse of even sand its grim. There should be gouges like bowls with low spots. Check your low areas. Lets see what others observe...
