Oh poor little guy......is he neutered? could be the reason why he is marking. It should be a perfect home out there for him, be very honest to any one interested and describe to them what's going on with him and the behavior with the previous families he has been with , that way it will help in finding the right person instead of getting returned every time once they find out the behavior issues. I'm pretty sure he is a sweet dog and with love , patience and the right training , he should come along.
Instead of a adoption fee , I would just be sure to screen really good and required vet references. Good Luck and best wishes to the dog in finding his forever home this time.
