How do I deal with snails and slugs?

I am trying to grow basil, sage (maybe breggarten?), and mint. I bought one pot of each 2-3 weeks ago. I put the mint and sage each in a flower box, and the basil in a (medium) flower pot. It's winter here (mainly rain and cold), so pretty soon garden snails and slugs started to eat them---especially the sage, with over half of its leaves now eaten. Since I plan to eat them, I bought a natural-based snail and slug repellent. It's based on some Gaultheria oil thing. It doesn't work. Slugs and snails just go to the planters' brim and bypass the barrier I sprinkled around them. I tried that old-wives tale of cooper wire. It doesn't work. And it looks like the copper barrier needs to be at least 5cm thick to work anyway (preferably 10cm and up). Salt isn't an option since it'll kill plants. Using synthetic snail and slug bait to kill them isn't an option either. I don't want to find out if it does break down and enter plants or not (and thus would enter me if I eat them). I am not willing to collect them every evening---both manually and by baiting them into a fake shelter. This is because I'd need to walk a good distance to get rid of them. It is both a major hassle for me, and those assholes have homing sense, so only a far walk would truly get rid of them. Even then it only culls their population. Since it's winter here, they laid eggs and buried them underground, so even if I cull the adults the next generation is already there.I started this whole ordeal to save some future money instead of buying (organic) leaves in some grocery store. At this point it's starting to get expensive; I'm on the verge of throwing them all out to cut losses. Only the planters belong to a neighbor that loaned them to me.What can I do?