Is every dropping like this, and how long has it been going on? Does he drink an excessive amount of water? If possible it can help to get his droppings checked by a vet for parasites. I would check his crop, his breast area for weight loss, and make sure that he is eating a balanced chicken feed. What do you feed him? A tsp of plain yogurt daily then twice a week can give some probiotics, and cottage cheese can firm up poops. The poop in the picture resembles some that I have seen in older hens with internal laying problems.