I've tried using/manipulating old copper piping after it was removed from a water system here, and it had marginal success. I think you need to have either a very even, flat surface or a small, specific area to target - would definitely work better as collars for pots than on the open ground for instance.

I like the shard barrier approach too since they're totally wildlife/pet/child friendly and, unlike pellets, don't need continually renewing after rain.

The best (and cheapest) I've come across are from Ecocharlie:

Slug & Snail Deterrent 2.5 kg

They use crushed-up/recycled ceramic shards which not only have the spiky deterrent factor but also absorb the mollusc mucus trail and so prevent the slugs and snails from moving across them.

We use Nemaslug nematodes too, but I like the benefit of something acting as a physical barrier that you can also see/feel/check on.