I know that Lynne is absolutely insistent on a fenced yard or area, so that would definitely be a no deal kind of thing. The fact that you have never owned a Dobe before really wouldn't have made much difference, if you had a fenced yard.
The reality is, if you want a healthy, well socialized puppy from a reputable breeder, or even a rescue organization, you will find that they won't let a puppy go without a fenced yard or area. Honestly, there is not much point in contacting any of the breeders mentioned here, unless you have a fenced yard or area for your puppy.
I don't think that is rude. That is, IMO responsible. It is not always possible to walk, exercise, etc. A fenced yard or area is truly necessary, particularly here in Michigan, with all the wildlife. Real easy for a dog to chase a deer (or the Coyote living on our property) and get in trouble.
When I started looking for my boy, I didn't have a fenced yard either. We live on 5 wooded acres and had no need for a fence. However, since I bred Aussies years ago, and I wouldn't place puppies without a fenced yard, I fenced an area. So, I could honestly tell breeders that I did have a securely fenced area for the dog. Nope, I don't have a fenced yard, but I do have a fenced area, off the back of the house that Wheeler has access to through a doggie door 24/7.
It is just the way it is, and I would be very leery of a breeder that would let a Dobe pup go without a fenced yard. That would tell me that the breeder's (and I use the term loosely), only concern is money. Which probably means that the parents haven't been health tested, pups is probably sold uncropped, etc.
While it may seem unfair and while most of us know people with dog(s) and no fenced yard, that do just fine. There are many, many, many not so fortunate dogs that meet an untimely demise because of the lack of a fence. (I worked for a vet for many years and have first hand knowledge of this).
Don't take it personally because it has nothing to do with you and everything to do with the breeders concern for the safety of their puppy. Thus, you may want to re-think the fence thing and do as I did... fence an area. (I bought chain link fence panels from Lowe's and for about $300 installed a secure fenced area).
Looking forward to meeting you this afternoon!