Hello and Thank You for contacting JustAnswer
I am sorry your boy is having trouble.I would love to help I just have a few questions.
What breed is he?
Is he neutered?
Any history of hip dysplasia or arthritis?
Is he on any medications?
When was he last seen by a vet?
What bland diet is he on and why?
Can you please review and answer the previous questions as well.
If walking while defecting is a new behavior for your dog then it is possible that this is due to pain in the back hips or knees making it hard for him to get into position. Arthritis and Hip dysplasia are possible causes.
Disc disease and spinal tumors can also cause all of the problems you are seeing.
Kidney disease can cause constipation and weakness in the hind end.
Adding some fiber to the diet may help soften the stools. You can add fiber by using Metamucil or canned pumpkin
Read more here,
Anytime a dog develops fecal incontinence it warrants a visit to the vet for a hands on exam and some blood work. As long as he is otherwise behaving normally I do not think this is something you have to do right away but I would suggest having him seen after the holidays,
I hope he does ok,
Best Wishes and Happy Holidays