This may help https://www.hometalk.com/3947849/organic-gardening-how-to-deter-slugs-and-snails-with-eggshells
I've used eggshells with limited success. I had to get real serious about snail eradication this spring because they were coming into the yard like an army on the march. I resorted to using a product called Deadline. It's a black liquid that you squirt to draw a line. When the snails cross it there's come kind of chemical reaction that kills them. I have also squirted the stuff directly onto snails and it kills them on contact. The other thing I do is keep a shaker of salt handy. Pour salt directly on their bodies and like Deadline it will kill them right away. Just be careful how much you pour as you don't want to add too much salinity to your soil.
Sink a few bowls or plates in the ground level with the surface. Fill the bowls/plates with (cheap) beer. The yeast attracts the slugs. They drink their fill and drown. Not their sorrows
Anything you can make it uncomfortable for the slugs/snails to crawl on will deter them. A combination of solutions from everyone here should take care of them.
Broken nutshells work in the same way as egg shells when getting rid of slugs. Break up the nutshells into small pieces, and create a protective barrier around your plants. Any slugs that come near your vegetables will soon turn the other way.
Crushed egg shells work as a great home remedy of slugs. This is because slugs don’t like moving across sharp objects, although it isn’t not impossible for them to do, they just prefer not to. Break up the empty egg shells into small(ish) pieces and place around the flowers, plants, vegetables, and fruits you want to keep safe from slug damage.
Ash and Cinders make a rough protective barrier, and the fine ash also acts as a desiccant that dries the slug out. Wood ash and cinders are preferable. Avoid direct contact with plants.
Grit and Gravel. The sharp rasping edges of finely crushed ‘horticultural grit’ makes an excellent slug barrier. Coarser gravel is largely ineffective, other than for decorative purposes.
Sandpaper. Cut rings of sandpaper and slip them round the stems of vulnerable plants.
Sawdust makes a good coarse barrier around tender plants, also acting as a desiccant that dries the slug out. Hardwood sawdust is most effective, and some people recommend cedar or oak.
Copper Rings or Discs. Solid copper rings/discs of various diameter, used to encircle single or small groups of plants to inflict a mild electric shock on the unsuspecting slug. Look for rings that clip together. These are easy to slip round established plant stems, or join together to form a larger barrier.
We (my grandmother) would get some ROCK SALT (ice cream maker salt) and sprinkled a line about 2" wide and about 1" deep around the garden perimeter. Before she placed the salt she would cut a small trench to place the salt in. The snails didn't stand a chance. She also did this around the outside door bottoms to keep the snails from invading into the house.
P.S.- her home was constructed in the 1890s and her doors almost touched the floor ( too low/tight to fit kick rails underneath the doors. when it rained the doors were VERY hard to open/close due to the wooden doors swelling from the moisture)
Hope this helps, good luck.