This happened to my old buddy Maverick (a Newfoundland, rest his soul). I came home one day and found a soupy mess in my kitchen. After letting the dog out, I went into my family room found a couple spots by the door. Then into my office...a huge pile of ****...I'm talking a medium pizza a full 2 inches high. Ugh! Called wife and said don't come home!
After cleaning all of that up, about 1/2 hour later, I thought I still smelled something foul.......went upstairs and

!!!! I think in a panic the dog was trying to find a way outside. Well, he pulled a 180* in the upstairs hallway spraying the walls, baseboard, even inside an electric outlet. What a friggin' mess.
If I remember correctly, some white rice and chicken settled his bowels and didn't have the problem again. I think he just ate something he shouldn't have (trash?) and got a little rot gut. If the shepard eats people food, or tends to venture into the trash, that could be the culprit.
Good luck with everything...as much as you don't want the dog doing it, imagine how it feels.