The only sure way is to pick them off the plants or wherever they're hiding, place them on a stone or slab and squidge them to obliteration. You can collect them in the dark by torchlight or just kill them whenever you find them. Some people put them in a jar of salty water to die, but I prefer the immediate satisfaction of the squidge.
A dry climate helps - we are in a very wet area
and we suffer particularly from a plague of snails. Snails though are easy to fling more than the necessary 18 metres to prevent them coming home.
If you use chemicals then slug pellets are fairly effective as long as you reapply regularly. I don't use chemical type pellets as they are so damaging to other wildlife. There is an organic version of the slug pellet which breaks down to a harmless iron product. I use this with good effect, but we have a huge queue of slugs and snails waiting in the wings to take over when that lot are dead. When I have used the organic pellets in my polytunnel, they tend to disappear on the first night - the pellets that is. We eventually found that the mice or voles were diligently collecting them up at night and using them to line their nests - very pretty décor, but not much use to me to kill slugs.
There are of course lots of deterrents but it sounds as if, like me, you just want to get the devils.