Stick to beaches which are also airfields of one type or another.
At least you can be sure that the surfaces will have been inspected for suitability on the day by people who know what they are dealing with.

The other major factor, which no one seems to have mentioned, is birds - always present, always unpredictable.

Don't forget that if you misjudge it and get stuck, you'll not be able to stop the tide coming in. It happened to a friend of mine. Choose your beach with care.
MB