Chickens love sand & will kick it around once they find out how much fun it is ~ you might need higher than a 2x4 board to contain sand. I put together a 4x4 cedar raised garden bed as a sandbox/dustbath for our chickens 10 yrs ago. There's a 10x10 popup canopy over it to keep sand dry during rain & shady during summer. No matter how wet or dry the yard is, the sandbox is always used by the hens.
However deep I made the sandbox, the hens fling the sand out of the box so we have to keep sweeping up the hurled sand & keep adding a new bag of playsand 2 or 3x/year ~ at least its not a real expensive item but those hens really throw that sand out when they dustbathe, walk out of the sandbox, then shake off the sand outside of the sandbox. Still, I'm glad we have it for them, just never knew they scattered it around so much! Sometimes it's just a nice place for them to snooze
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