Recently I read trade magazine about why homeowners insurance exclude certain dog breeds. Apparently 1/3 of all homeowner claims are dog related and an average claim is $33,000. The standard list of 5 is: Pit Bull, Rottweiler, Doberman, Presa Canario and Chow Chow.
Many dogs do not exhibit aggressive behavior until the day they attack.
It's complicated and simply riskier if a homeowner owns one of these dogs. Many companies will require an exclusion or simply will decline an applicant due to the aggressive dog exposure.