I’ve heard that snails and slugs will avoid broken egg shells and therefore that they (the egg shells) can be used to protect seedlings. I tested this claim by putting a snail out on the dirt and in the sun surrounded by broken egg shells. As you can see by the image the shells didn’t work.
I’ll run this test again once I get more shells with which I’ll make a more robust barrier.
(I wonder if snails would be similarly deterred by a ring of crushed snail shells?)