Dehydration is a big cause of constipation. Do you feed dry food? This could certainly be a reason for it if you do.
Tony
Pumpkin is good but not too much too much will make it worse
Hi, I can give you a couple of ideas. You don't say what you regularly feed or what type of dog.
You can give canned pumpkin (NOT the pumpkin pie filling) added to the food or try some straight a couple of times a day.
You can add some *mineral oil* (not cooking oil) to the food to help lubricate the stool. Again, not sure of the size so I would only maybe use 1-2 tsps.
You can add Grape Nuts Flakes to the food daily.
You can add Bran Buds to the food daily, both as a source of fiber.
I hope the dog is drinking.
Just a note, are you sure there isn't possibly an anal gland problem?