How far do I plant this bulb in ground?
I believe that you have a Colocasia bulb. There are several plants that are given the name of Elephant Ears. They are all in the arum family. In the Colocasia group there are clumping and running forms--the runners are called stolons.
Your bulb looks to be one of the running Colocasia bulbs.
These bulbs should be planted 8-10" deep.