Some other possible approaches:
Hanover Slug Fence
http://www.slugfence.com/
Electric Slug Fence
http://www.cleanairgardening.com/slugsaway.html
Videoclip of slug encountering two-strand electric fence
http://www.youtube.com/watch?v=OQeGSPH4wrQ
Longer videoclip of same
http://www.youtube.com/watch?v=KYPdTNya3Q0&NR=1
These slugs appear to be larger than the ideal vector slug expanding its range in Hawaii; for this approach to work may require placing two wires closer together (as via manufacturing a tape or integrated-circuit-board-like strip with tight quality control on the spacing tolerance of the two exposed metal surfaces).
An idea I am interested in testing is to combine a physical barrier with a passive electro-chemical countermeasure. If you scroll down to the bottom at this site
http://www.slugfence.com/slug_info/body_slug_info.html there is a
cross-section of a Hanover Slug Fence. If one were to take C-channel and bend the top down at an angle then it is close to looking the same. If one were to size the lower channel of C-channel such that the now-inclined upper channel were to overhang the lower (yes, this would probably mean one needs to fabricate the customized channel of flat sheet metal, from scratch, not just bend existing C-channel) then the lower channel would be protected from rain and could be filled with a salt solution. Rocksalt brine &/or maybe some copper sulfate depending on toxicity issues depending on what (chickens, etc) or who (toddlers) might get in there. Even if the brine dried out and was a crystalline residue in the channel, when a wet slug encounters the residue it should still have an effect. If the barrier is made of zinc and a copper wire is run around the inside through the salt solution then whenever moisture is present in the system a weak electrical charge will be present.
Another notion which has occurred to me for testing in situ once the greenhouse is up is to rig an anti-slug laser system around the raised beds. If it turns out that the slugs are repelled when they encounter a 5 milliwatt (mW) red or green laser then such a laser barrier would be inexpensive; 5mW lasers are about $40 to $60 and mirrors are not expensive. Theoretically, just one laser could defend an entire greenhouse all night long if the mirrors were carefully aligned to adroitly bounce the beam around a pathway surrounding the raised beds, although it would be much easier to have several lasers and not spend so much time periodically realigning mirrors. There is doubtless some way to rig a photovoltaic panel in combination with a rechargable battery bank and a sensor switch such that the array recharges in the day and is active at night. If a higher wattage is needed to deter slugs then very impressive green 15 mW lasers are available for around $100 -it would be surprising to me if a slug would crawl through a 15mW laser beam (the effective range on a 15 mW beam is six miles; they are dazzlingly bright). An awesome 300 mW green laser is available for around $2000 (that is, not even the cost of one trip to the hospital for rat lungworm) but there would be complications with needing locks on the greenhouse and eye protection up in that relatively huge wattage -and 300mW probably way more than is needed anyhow. Here is a source:
http://www.wickedlasers.com/
Some notions will crash and burn, perhaps even most of them. This is to be expected; we can learn even from those efforts which fail ("fail" in the sense of not turning out to be a silver bullet). If anyone is interested in networking to exchange ideas and getting together to assist each other in tinkering and cobbling together various devices and systems for testing anti-slug approaches, then please do contact me. It will be awhile before my own greenhouse is up -and besides, it is perhaps naive optimism or even hubris but I hope to so successfully suppress the slugs and rats at my place that it will be tough to test different methods for lack of available test subjects. If you are in a slug &/or rat infested neighborhood and want assistance then maybe some of us willing to serve in a Science Wizard Brigade of sorts could come and assist you to design and rig a system of one type or another at your place. Seems like if we focus and combine our collective attention on this problem then via testing out a variety of innovative solutions we will eventually figure out a set of options which offer significant protection, especially if several overlapping methods are used simultaneously.
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Vienna Teng in Düsseldorf, "Soon love soon."
http://www.youtube.com/watch?v=v8-mIouMbqM
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