im sure dogs do it for a laugh..my dog will shite where i dont want him to...he will have a crap as soon as i finish cleaning the yard out, im sure he holds it in till i do..or when we are out for a walk guaranteed to want to lay a burger outside someones door, unlike most dogs that would crap on the field he has been running about on.. and although i always try to pull him away there is NO shifting him..its like hes been stuck in concrete the big shit machine