What are some DIY ways to deter or end slugs in the garden & planters?

Place dishes with beer around the plants.

https://www.rentokil.com/blog/10-home-remedies-for-slugs/#.WsVekmaZPR0

I am battling these guys in my garden as well!

https://www.wikihow.com/Get-Rid-of-Garden-Slugs

At garden store you can buy slug repellent. But the beer as answer 1 works really well. Just remember to empty your container

https://www.thespruce.com/slug-control-in-garden-1402502

I save egg shells. Break them up into little pieces. Put them in a line. They will not cross as it cuts their bodies up.

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.

I read beer in a saucer draws them and they drown. But I have not tried it.