Dogs should be fed only once a day for adults. Dog tend to eat at certain times of the day as well. You will have to figure out what time seems the best. Mine will eat mostly at night. Don't want to leave the food out too long as it can form worms/maggots in it. Watch out for can foods. They are higher in calories. Dry foods are better for teeth health and for less poopy.
Take him to the vet to make sure it isn't worms or other intenstinal distress. Has the weather changed? My dogs refuse to go out in the rain or really cold. I put 'painters plastic" down on my carpeted floors.
Again, check his diet, environment, or other behavioral changes. This should give you clues as where to look to fix the situation.