Neven,
Have the slugs paid for the electric fence you built to keep the buggers out?
I sometimes find euro coins in the garden, but they may have dropped out of my own pockets.
The fence keeps out most slugs (especially the big ones), but like silkman says, just one small slug on the inside in autumn, and you'll have dozens in spring again. Also, the fence needs to be maintained, which means weed removal and checking the wires don't touch anywhere. At some point I will build an improved version. Of course, the slugs will have to pay for that one too.
One mistake we made, was keeping a couple of fixed plants like oregano - and we left some coriander standing - within the vegetable garden perimeter. Even though I had dug the garden when it started freezing at night (not happy about that, as I like the no-till philosophy for optimal soil fauna), the little buggers returned in early spring. The small white ones, not the big brown ones. Especially the coriander offered refuge, it seems.
They are mostly a problem during April, May and part of June, when seedlings are small and vulnerable. The slugs also seem more hungry and active then, and so we went out every evening with a flash light to kill as many as we could find (dozens of small ones). Then, at some point, we removed all the hay mulch, did some more hunting for three evenings, and then put new mulch in. That really helped a lot.
Now that most of the plants are big, we don't check as much. There doesn't seem to be any major damage. Flea beetles and caterpillars are more of a threat now, so we focus more on keeping them in check. We've learned a lot from last year, especially my wife, and so we recognize pests earlier, which really makes a difference. Damage seems a lot less this year.
For next year we'll remove all the fixed plants, probably do some tilling to further improve the soil, and then do the same with replacing the mulch at some point.
Speaking of hay mulch, the potatoes we planted in them were more of a success than expected. I wasn't sure if the layer of mulch was thick enough at some point, and as there's no electric fence around the potato plot, there was an orgy of huge brown slugs every evening, to the point that the plants didn't even have flowers. I checked once under the hay and there was only a hull of a potato, so I figured the harvest would basically be zero.
But turns out I was wrong. We planted 5 kg and got 40 kg out! One third of the potatoes had holes in them, some of them still containing burrowing slugs, but the rest looked pretty sound. Too bad we don't have a good way to store them. Looks like we'll have to build a small root cellar at some point.
Next year we'll use even more hay mulch, and maybe get some ducks. I'm quite pleased this works, as digging potatoes is quite a lot of work.