Copper? (Copper bands and copper tape)
Slugs and snails do not particularly like copper but they will cross if they want to. Just see our video or do the experiment yourself. Fix tape around the inside of a pot, put some snails in it and leave overnight (when they are most active). See how many are left in the morning.
However, copper oxidises and becomes even less effective.
This explains why people find that copper does not really work.
Furthermore copper in large amounts is toxic (which is why it is used in fungicides) and tape leaves a nasty sticky mess on your pots at the end of every year.

Pellets?
These methods are not good for the environment.
They are deprecated by every wildlife organisation.
Do you want to be part of polluting the water table? Our grandchildren will not thank us for all the poisons that we throw around.
Form a practical point of view, each time it rains they disappear so need constant replenishment.

Grit?
So slugs and snails don't like grit? Maybe, but something sharp isn't necessarily a deterrent. Click here to see the evidence on one of our cactii! They may not particularly like grit and go around it but, after millions of years of evolution, is it realistic to think a couple of inches of grit are going to stop them?