I have had a futile battle with molluscs - and have tried all forms of guerilla warfare but, fwiw, I will add my patent hosta protection to the list (and it shocked me that it appears to work) - using old pennies as a mulch. In the UK, 1p and 2p coins - perfect...and they looked surprisingly stylish - almost (I hesitate to say) classy. And seemingly, the snails hated the idea of an entire march of grief because, for the first time in the history of my garden - no munching occurred.

Yes - Campanula, as you say a futile battle. Note that the OP is in California. I suspect that people don't even begin to understand gastropod trouble there. So many of the 'remedies' suggested in these kinds of articles have absolutely no effect in our climate. Diatomaceous earth, for example, doesn't work when wet, ha, ha.

I might try the pennies though. But you said 'old' pennies and then said 1p and 2p which are new pennies. Which did you mean?

Oh yes! I've read about the pennies somewhere but totally forgot about it. Will make nice pretty rings around my seedlings, and cheaper than the copper tapes.

Here's John Oliver's take (down) on pennies.

Apparently, the old pennies have a higher copper content than modern coinage...but I used a selection of 1p and 2p coins, overlapping and covering almost the whole top of the pots...and was astonished that last year, the 2 measly hostas were uneaten.

I have only one measly Hosta. I'll give it a go this year maybe.