I live in an oceanic climate so there's plenty of rain. In our garden we have lots of slugs and snails. When I first searched about this topic, I was amazed how many ways people invented to keep the slugs off their yard. Well, I tried most of the things suggested from beer traps to placing brumble cuttings around the plants to repellent substances from essential oils, you name it. None of them really worked.
As the permaculture saying goes, you don't have a slug problem, you have a duck deficiency. If you have the chance to keep ducks, indian runner ducks are appearently great at controlling the slug population. And very importantly, this type of duck doesn't eat your plants. Some of my friends have them and they have no problems with slugs any more.
Unfortunately, keeping ducks was not an option for me. The solution I figured for my situation is what I call the night hunt. Every other day or so, I go out to my veggie garden during the night before going to sleep, and collect the slugs and snails in a bucket and put them in my in-situ compost bin. This drastically removed their number. It requires constant management but so far that was the only thing that really worked for me.