> Use AC, i.e. 12VAC, so the wires won't be eaten away ?

Yes, if you can. I made an electric fence to keep snails out of the
veges. It was a border of upright 6" planks with two wires around,
1/2" apart. Originally I had 12V and 0V but the wire, even though
it was galvanised, corroded quite quickly. I replaced it and switched
to AC and had no more problems. A couple of seasons later I had
to do the same to a location not within easy reach of power, so it
had to run off a battery. I made a retriggerable one-shot driving a
trigger transformer. 5ms every 5s as I recall. Worked just as well
and 4 * D batteries lasted a very long time

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