This morning, I had a lovely email from the people who make those copper slug rings concerned about what had happened to one of my mini hostas - chewed to the stalks despite having a slug ring around it. Their suggestion was another slug ring around the base of the pot since, and I quote them, 'protecting hostas is the most problematic - they are like caviar to slugs and snails'. I'd agree with that. They go on to say that slug rings are not 100% effective - they get about 95% every season. That's a pretty good average - I could live with that. Here's their photo of a beautiful hosta with double protection.
Now copper slug rings aren't cheap but they do last for years. Another suggestion is just to use the one round the base but I think what's needed here is a 'belt and braces' approach especially with the most beautiful and succulent hostas - to the snails and slugs that is! And you have to be absolutely scrupulous about making sure there is no way that they can vault from one nearby plant something that's easily forgotten about later in the season.
Where I am having total success with them is round my sweet peas. The smallest size ring is perfect to pop round the new young shots and easily removed later in the season once they are established. They shall not win!