Scattered crushed egg shells are a good deterrent for slugs, because they cut their bodies.
A permanent solution
To rid the garden of slugs and other pests permanently, the fertility and drainage of the soil need to be improved. Pests thrive in poorly drained, infertile soil. Enrich the soil with plenty of compost, and even more dried leaves, to making it water-retentive. Pests will all migrate to soil which is more to their liking. Forget about sprays. Spend that time improving the soil and you won't need to worry about pests next year.
Slugs in container gardens
Organic Gardening magazine recommends protecting container plantings with copper coins or tape glued to the container, but if the container soil is as water-retentive and well-drained as it should be, there is no need to worry about slugs.
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