Inspired by his daughter's penchant for putting live snails in her mouth, as well as his own magnanimity toward his garden's slowest pest, Redditor WHELDOT constructed a DIY electric fence that deters snails without killing them.
In a demo video, the snail inches slowly toward the wire and touches it gently with its soft mouth until, ah, geez, its zapped by nine volts of electricity. Its whole face puckers in, but don't worry: it would take more voltage than that to toast this little guy. Nine volts is just enough to make it think twice.
There's an older Instructables for this, as there is for just about every endeavor known to man, wherein a gardener makes a similar electric fence to keep slugs out of his raised box. He's got schematics:
Common solutions for snail invasions include molluscicides with names like "Deadline Force II" and "ELIMINATOR," which—aside from being overly aggressive for a foe that's made mostly of water, soft tissue, and protective mucus—can be toxic to pets or kill the plants you're trying to save. As we've established previously, it's hard to say whether invertebrates feel pain like humans do, but at least a jolt to the face won't leave them to the fate of toxic organ failure or death-by-dissolution.
Snails and slugs everywhere thank these valiant gardeners for their humane efforts.