Unfortunatly it's getting to be like that all over. Most places in Oregon, New York, Arkansas & Florida just that I know of personally, are like that. Sadly it is because rotts are one of quite a few breeds that are listed as "dangerous" breeds. It is very difficult & expensive to get homeowners insurance with the breeds on the list, therefore most people that rent out homes can not afford to have insurance with one of those breeds.

A few tips to rent a home with one of the breeds (ussually private owned rental homes are easier to get into than say a large apartment complex):
Give them all vet records to show you are a responsible owner & keep up to date w/ the dogs vaccines & health

Make out a resume for your dog

Give them statements from people (old neighbors, vets, dog trainers, family, friends etc..) stating your dog is calm, quiet, friendly

Show all graduation certificates for all obedience classes, agility classes, CGC (that one really helps) etc..

Offer to get your own renters insurance that covers your dog

Offer a larger security deposit

Have them meet your dog in person

Offer them to stop by frequently to make sure your dog is behaving properly, &/or make arrangements for the (future) neighbors to "report" to the home owner every once in a while with an update of your dogs behavior & personality.

If it is possible to take your dog to work with you then tell the home owner, then 90% of the time the dog will not be left home alone.

Tell them you are willing to crate the dog (if you don't already do so) when you are not at home

Good luck