You will probably want to avoid using Cocoa Mulch.
Going to the snopes website and doing a search on cocoa mulch returns information, last updated in 2009, about the dangers of this mulch which contains Theobromine.
This is the ingredient in chocolate that can cause death, particularly in dogs.
Here is a link to information about this brand of mulch, showing the presence of Theobromine.
One suggestion in the article says that 98 out of 100 dogs won’t eat, but that of the 2 that do, one will suffer physical harm, including death. The odds are still too high.