12/2 UF (underground feeder) cable is the thing to use, it has two main
conductors (black/white) plus a smaller ground wire (bare or green).
This looks like the stuff usually known as Romex, but is meant for
ground burial and weather resistance.
....
You should run some red plastic tape, in the trench above the wire, so
that someone can notice BEFORE they dig into the cable with a shovel.

Any chance of that and you should use conduit.