Jocoyn ! this is exactly what I have and my comment would be that the belt is NOT long enough for the stride of a GSD . Front paws of an adult land in the gap between the belt end and the wood frame .
Also the belt seemed to wear rather quickly.
The dogs loved it though. I have it set up in my barn and all the young pups will race to it and get started on their own. For young dogs okay! Adults -- well I am looking for something longer myself - I liked the one that Sunflowers was using. shipping adds quite a bit to cost.