Copper strips are very very effective but very very expensive. You can really only use copper on pots to keep the slugs from creeping over the edge. I've found that the hate lemon peel and orange peel, but it's not the prettiest thing to have scattered around. Some people find that those bags of cocoa chippings from the garden centre work well.
If you have a compost heap, you can put any slugs and snails you find onto the heap. They will help the worms and woodlice to break down all your kitchen scraps and old newspapers. Putting a bit of black plastic sheet on top of the heap will encourage them to stay there where there is lots for them to be getting on with and they won't be so tempted to go looking for your plants.