keep shells in open container in fridge. When full, crush shells into small bits and sprinkle around base of plants. Sharp eggshells will deter slugs, snails, and other bugs from nibbling on garden and add touch of calcium to soil.
I like use of rocks gravel to slow water down as it moves through landscape on slight slope. Flat stone with depression in foreground a perfect spot for bees & butterflies to get water (without drowning in a deeper birdbath)