Our Small 7 Yr Old 10 Pound Mix Breed Just

Our small 7 yr old 10 pound mix breed just started having fecal accidents in our home. we thought it may have been something he ate outside but concluded that was not it. Sometimes the fecal matter is normal looking and proper consistency, other times it is a little runny or gelatenous and with a greenish tint. We feed him only dry dog food with occasional moist food and he has plenty of water. Thank you