Try growing your own Nemadodes (not for the squeamish)
I have been experimenting with growing veg in straw bales , on a sheltered but sunny rocky ridge that does not have enough depth of soil for conventional gardening. Unfortunately the organic matter content has also caused an explosion in our slug population, despite beer traps & daily slug picking, & the veg has been decimated. I am reluctant to use slug pellets. At the time, a problem with the production of commercially available nematodes to use as a biological control in the UK meant that they would not be available for at least a month, & by then the surviving veg would have been destroyed.
Then I came across an old article in The Telegraph that really seems to have the answer. Their solution? Take a jam jar & punch holes in the lid, add 10-20 live slugs, a handful of grass, & half an inch of water, then replace the lid. After a fortnight, all the slugs should be dead. Mash the whole lot up, dilute with water & spray onto the affected soil. Should give coverage for 6 weeks in much the same way that commercial nematode preparations do.
The grass gives the slugs something to eat, & a way of staying out of the water & not drowning. The water stops them dehydrating. Holes in the lid stops them suffocating. Confining them means that when they die you have access to the naturally occurring nematodes & internal parasites inside the slugs that would normally build up over time, & may also stress them allowing a bigger than normal build up inside the slugs, concentrating the nematodes & parasites that you want to harvest.
I used bigger containers (2 & 4 ltr plastic milk bottles), & 60 + slugs at a time as I had plenty available. After a fortnight the slug mixture really stinks. I mashed the lot roughly using a bucket with a stick, added more water & spread the mixture using a watering can without a rose, squashed corpses & all. Miraculously, it really seems to work & I am seeing a big improvement in my veg. Am planning to carry on picking up & confining any remaining slugs I find, & spread a fresh batch of slug mixture every 6 weeks over the spring/ summer & do a pre-treat on my seed beds next year.