Dwarf puffer fish - $1.99 at any Petco. Cute little fish with a thug personality.
They are somewhat aggressive to each other. Not much, only to the point of killing each other if you bought too many and leaving only the partners they like. Once established in the tank the puffers are very hardy and the only downside to them is that they will nip the tail and dorsal fins of other (slow moving only) fish if you don't feed them enough.
I think Mr Amano uses dwarf puffers to eat snails, when the need arises. The puffers are moved on when the job is completed. If you have storage accomodation for the sometimes pugalistic puffer, so be it.
Sometimes a simpler method to eradicate snails is, for instance, to put a small leaf of lettuce into the aquarium overnight and remove it along with the snails it has attracted the next morning.
Or, use a narrow-ended siphon tube and reduce numbers at every water change.
I have tried the lettuce trick, only I used cucumbers. It actually works really well as suppression tool but won't completely fix the problem. You also have to be carfull if you have beneficial snails. The trumpeter snails I think are good for tanks because the burrow into the soil and help to aerate it and they don't eat plants.