Copper tape

It's possible you already have slugs or at least slug eggs in the compost in the pots though. I'd use nematodes and the copper bands if you already have them. I think it does help where you don't have too many of them. In my garden they move in such numbers that there' always one ******* that crosses it, leaves a trail just to tease you and proceed to munch the whole plant.

I swear by nematodes.