This is a great place to come for all things dobe. If I say so myself
When you say a dog could go around your fences, do you mean that that is place where you can walk her, or do you mean she could get out and be loose on her own? Because if she can get out on her own, rather obviously, you'd have to find a way to keep her safe.
Dobes are definitely indoor dogs--they like to be around their families and aren't very happy when left alone out in a yard. In addition, they are rather sensitive to heat and definitely sensitive to cold temperatures. So you would need to be planning on keeping your dog inside, whether or not you are there.
She will need exercise every day...minimum a couple of brisk miles on leash. It's getting harder and harder to find a place where your dog can be off-leash safely and legally, but you should not depend on using a dog park as a place to exercise your dog. Dobes can be dog-aggressive; as adults, they aren't particularly interested in being around other dogs to play. And if you do have any altercations between your dog and another, you can count of the dobe being the one who is blamed, regardless of how rude the other dog is, or how irresponsible its owner is.
One way people keep their dogs happy and entertained is to start up some training/sport with the dog. You definitely need to go to a basic obedience class just to teach your dog manners (and adding a puppy class is great too.) Even if you know how to train your dog, just having a controlled place to work with your dog, teach her manners and to accept all kinds of strange surroundings and people (which is the first step to having a balanced dog), AND have the resource of a teacher who can catch bad habits BEFORE they become habits
, and give you advice when you run into a behavior you don't know how to fix, is invaluable.
But it's an added benefit to keep working your dog...maybe agility, higher obedience work, scent work, dock diving, tracking--even protection dog training (if you're prepared to put a LOT of work in). You and your dog build a better bond; the dog gets brain exercise as well as physical exercise. Everyone wins. A chance to use her brain is really important for a smart dog like a dobe, and you'll find that that exhausts her as much as physical exercise does.
I'll leave my dissertation at that. If you decide a dobe is a good dog for you and that you would be a good owner for a dobe, then the work of finding a good breeder begins. Yes, you definitely want to get a dobe who can be registered...that is part of what shows you that the breeder is reputable...but that is just the beginning. I'll let other people say more about that, though....this post is getting long enough as is.
Again, WELCOME. Stick around, ask questions (it's so good that you're doing that BEFORE getting a dog), talk about yourself, tell doggy stories, whatever
We're glad to have you.