It sounds like your dog has "tenesmus." It is often seen with colitis, and it causes loose stools which are productive during the first bouts, and then they become scarcer and scarcer with the dog emitting only a few drops of liquid poop, possibly accompanied with mucus and blood. If your dog has loose stools, you will likely need to take care of the diarrhea. Since your dog is ten, it would be best to see your vet so to determine the cause of the diarrhea. Your dog may need meds to fix this. Fasting the GI tract for 12-24 hours and then feeding a bland diet for a few days may help mild cases.