It all really depends on the plant, aroids are as diverse as it comes. Although Colocasia specifically grows from a tuber I am not sure if it makes runners or underground offsets. Either way if you dig the plant up this fall im sure there will be loads to divide up.

Here is a link that might be useful: International Aroid Society Forum

They make offsets as they get bigger just little plants beside the main one. Separate them once they get a little size...