My son has said Doberman and heard many "clicks" followed by a dial tone over the years. To that end I'd like to offer a few suggestions which will hopefully prove helpful: 1) Find a rental agent who knows your situation upfront. They can zero in on properties and private owners who may be more liberal in their thinking when it comes to large breeds. 2) Offer a pet deposit or increase the amount of the existing deposit requested, 3) Purchase a liability insurance policy for your dog naming the property owner as Additional Insured. Policies are not expensive and can make all the difference! 4) Offer or increase the amount of "pet rent."
Wishing you the very best of luck!
Also you can try approaching your vet; explain that you are having difficulty with finding a place to rent. If your dog is a mix they will many times agree to change the breed mix on the paperwork.
As long as it says so on the papers many places will accept that. For example, I know of someone who has a breed mix that was discriminated against ; he got the vet to state a different breed that most people do not know.