Now I will admit, I am no fan of slugs but I have changed my mind a bit on the critters and here is why:
The last few days have seen me either glued to the TV with my eyes or the great white bowl with my butt, and I happened to be watching a Nat. Geo. show about the internconnections of nature. This program happened to be about the rain forrest of the Pacific NW in USA and included a Banana slug. This slug happens to eat, among many things, the remains of dead salmon that bears don't eat. That slug then moves away & leaves a trail of mucus that is loaded with nitrogen, which in turn, helps the plants & trees in that area.
NOTE: Heavy rains wash away most of the nitrogen in that area and end up in the ocean, which plankton eat and salmon then eat in their turn. Birds & bears then eat salmon and they poop out a small bit of nitrogen. Fungi, flies, and slugs then feast on what remains of salmon, and then they poops and birds & other critters eat slugs and so the cycle continues.

So then I checked out slugs world wide and found out that they all do the same thing in their own areas of the world. Return nitrogen to the soil!
They, among other critters, are a key link in keeping the soil just right for plants & trees to florish.
Sure they eat what we don't want them too, but then again they eat stuff that we do want them to do also. Like weeds, dead critters, etc. So what to do about keeping them away from our favorite plants without killing them outright and letting them do their job?
It seems that the right way to do this is sprinkle down a barrier of salt- not on the slugs cause that will kill them, but around your favorite plants etc. Yes! That barrier will have to be renewed after each rain but it does work.
Another method is put the plants out of their reach- if possible. hanging pots etc.
The last method is: Just let the slugs eat what they wish cause they are giving you soil that is full of nitrogen which is great for your soil & plants. So the cycle goes!

There is another method though: Dig up all your plants & plant rocks!