Look into food grade Diatomaceous Earth. It's a natural repellent, harvested from the sea and adds a nutrients to the soil.

If you go for that, make sure you pick one that's formulated for garden use.

That's what we're talking about.

Personally I'd just use metaldehyde pellets, sparingly scattered. If you buy Erazer ones, they're rain proof so you don't have to apply so often. These are attractive to eat for molluscs like slugs and snails, but nothing else eats them. And no, they don't kill birds, or hedgehogs, well, not unless you leave the pack outdoors and a hedgehog eats half the pack in one sitting. As for pets, obviously its best if they don't eat them, but the odd one or two here and there won't kill them anyway. You'd need to be careful with a Labrador and similar breeds, because they tend to eat anything and everything, so storing the pack away carefully is important.

Diatomaceous earth is available for garden use now in the UK - however, it also must be used very sparingly because its not discriminating in the way it kills, and will kill any organism it comes into contact with, including the micro organisms and larger ones like worms in soil that you don't want it to. I wouldn't use it where there are pets which might venture onto the borders, I consider it worse than slug pellets from a pet's point of view. More info here re this product

http://www.slugoff.co.uk/slug-barriers/diatomaceous-earth

There's a link on that page to Nemesys products - there is one for slugs, but its ineffective for snails. The choice, as they say, is yours!

copper also seems to work. I put a ring of copper pennies around each cabbage plant, not a single nibble in sight. That's another option. Diatomaceous Earth is also an excellent fertilizer with many trace elements vital to healthy plants.