Shake some salt on the slugs. As with other soft bodied animals, it dehydrates them and they die. Be careful about adding salt to the garden. Better to collect them into a container and salt them in that. Better still, kill them some other way and add to compost or feed them to the plants by burying them near the plants you want to feed.
Wood ash kills slugs on plants by absorbing their moisture.
Will be dead in minutes. Be careful with ash though as it will vary the Ph levels. Crushing egg shells and putting around the plants controls snails. Keep the egg shells in the frig for a day or so as they crumble better. Just watch it doesn't cook the plant though it which case it will meet the same fate as it would have had it been left to the snails.