If my dog were over 2 years old and still lacked impulse control I'd seriously focus on teaching it and put aside anything else we've worked on. Lots of small increments, lots of baby steps, lots of going back to square one even when he doesn't need it just to keep the pressure off.

Sounds like a headache and lots of frustration. Dobermans are usually very smart, but there are plenty of dogs that are 'dumb'.

I've been thinking about how you asked 'is it like horses.' I think it's not, because horses are flight animals and hold onto things. A high level show horse going through the woods gets spooked by something new and 'scary' and then has a complete melt down in the ring because he's still holding onto it. It can take a lot of work for flightly, nervous horses to be able to let things go.
Dogs aren't like that. If he's being impulsive and disobedient out in the real world I'd severely limit his interactions unless you're specifically working on his problems and know that you can continue to keep his focus.

Cheri;

I have exactly the same issue. My dog was 2.5yo when I got her, with NO foundation at all. She is not well-bred, though she has some solid working lines scattered through her pedigree. She has always been a house/yard dog, tasked with guarding the property, so she has always been left to her own devices for the better part of the day, and thus has always had plenty of time to "just be a dog", and practice self-gratifying behaviors. She also enjoys fishing trips and romps in the woods, and the occasional loose-leash stroll through the neighborhood.

Now, just a little over two years later, she has pretty solid obedience, and loves marker and schutzhund training. She learns new behaviors quickly, and absolutely loves some of the activities involved with the schutzhund training (dumbbell retrieving, obstacles, etc).

However, her focus is just not as good as the more serious sport dogs we encounter. Part of the problem is lack of a strong prey drive, and, IMO, all of the self-gratifying behavior that is so solidly rooted in her upbringing. We work on focus religiously, but her progress in that regard is slow. I get so jealous when a young dog with super-high prey drive comes out to the club and heels better than us, and it makes me push her more, but the focus is still lacking.

In my circumstance, and possibly yours, the foundation for that type of focus was not imprinted at an early age and her breeding is not helping. You said your dog was from showlines. If I were obsessed with having a top-tier competitive dog, I would get the best working-line pup I could afford and start from the very beginning, building on that focus. With the dog I have, I am content to help her be the best she can, and enjoy the wonderful companionship that only she can provide.

I own another Dobe, and the ironic thing is she is a BYB rescue, acquired when she was a year, year and a half old, and she did indeed come with baggage, primarily a lot of fear issues. I've shown and titled her in both rally and obedience. She's come a long way.

My hyper-excitable guy is one I've owned from a pup and he's from a reputable breeder, so if anything, I expected he would be the easy one and the rescue would be the challenging one.

So, as suggested, we will go back to the basics again (and as many times as we need to) and hopefully we will make slow, steady progress, but for now I'm setting aside the idea of getting him in the obedience ring. We'll just wait and see. I still have a nice dog and there are many other enjoyable things we can do together.