As an aside no one has mentioned beer traps. I can assure you they catch slugs in huge amounts. Alas not enough to give full protection to your plants.
Disposable coffee cups can be used successfully as they are plastic coated. They don't last forever. Put holes in one cup put it inside the other. Cut holes in the sides, part fill with beer. Put lid on. You can remove slugs without wasting the beer or pulling up the trap and have to dig it back in again.
Something plastic is better choice if you want something a bit longer term than the non disposable cardboard coffee takeaway cups. Margarine tubs?
Also putting something down for slugs to sleep under during the day catches loads of slugs as well. I may try some pallet bits.