Dark Rum Substitution:
"We have no idea what you're making or how important the rum flavor is to the finished dish, so finding an acceptable substitute is going to land mostly on your shoulders. You can try water, white grape juice, pineapple juice, apple juice, or apple cider. Your recipe's call for dark rum, though, is surely an indication that it wants a lot of flavor, so all of those may fall disappointingly short.
Rum is distilled from molasses or cane syrup, so your best bet could be a mixture of molasses thinned with pineapple juice or white grape juice."