Your concern for animal cruelty reminds me of a story from many years ago.
A vet was offering the service of castrating camels for 100 Dinar; a local owner accepted this offer to castrate five of his camels. The owner observed the vet carrying out the castration procedure which consisted of the vet banging two large bricks together with the camel’s testicles between the bricks.
Concerned at the potential pain – the owner asked if castrating the camels hurt at all, to which the vet replied ‘Only if a catch my fingers between the bricks’.
Beer traps are quite a good idea. Fill an old coffee cup or the like with cheap beer and sink it up to it's neck in the soil. Slugs can't resist and they die happy. If you know anyone who keeps poultry, the chickens love them.
I worry about what might come along and eat a poisoned slug, so don't use the poisonous pellets.
I found that spent coffee grounds are a good deterant.
I did say scattered around, Diddly....of course you don’t put the pellets directly onto plant.
Heavy rain will cause the pellets to leach into the soil that is feeding your growing plants.
Looking on the Net and finding lots of opinion but no clear info, there seems that there are pellets, and there are pellets. This Amazon.co.uk User Recommendation I found on Amazon claims that the slugs go underground to die, are pet/animal friendly (except slugs I guess) and break down safely in the soil. I guess the trick is to read the box.