Well you all think you know everything about dogs, then why are YOU guys here, asking questions? I did not exactly post my concerns here because I wanted advice on how to fix the problem, but I wanted input about what may be causing this behavior.
I don't think I know everything about dogs. I don't think anyone here believes they know everything about dogs. There are many people on this board who are quite experienced, many with more experience that I have.
I am a trainer, I teach classes, I compete with my dogs. I always have something to learn, and I enjoy helping others who have less experience.
IMO, what is causing the behavior is that he is a puppy. Puppies get scared of things, sometimes for no reason other than a fear stage. As was mentioned by others, it's not uncommon for doxies to be uncomfortable on grass, so breed is a factor.
I also believe that forcing him into situations that he's already uncomfortable with do more harm than good, and while he may give up and go on the grass and up the stairs, there is something called learned helplessness. It doesn't mean the underlying cause has been solved. Forcing him into uncomfortable situations does a disservice to building trust, which is necessary in order to build respect.
Using positive methods, creating positive associations with things that he's unsure of or uncomfortable with don't create a spoiled out of control dog. They create a dog who is enthusiastic and confident. A spoiled dog or an out of control dog is a dog who hasn't been taught boundaries. Boundaries can be taught without the use of force.
As for dominance, a true alpha dog doesn't intimidate with punitive acts. An alpha dog relies on body language to create a presence, an alpha dog projects confidence. Pack structure beyond that is dynamic. Much of old school pack theory has been proven to be erroneous. The old school pack theory was based on wolves in captivity. Wolves in the wild behave differently from wolves in captivity - in captivity, they are required to inhabit a much smaller territory and that caused dynamics that weren't seen in the wild. Pack theory based on wolves also doesn't equate well to domestic dogs - a species that has been selectively bred to live and work with people for centuries.