In Wisconsin, do therapy dogs fall under the ADA? Tenant provided a prescription from his therapist for a "therapy" dog.

Therapy dogs are covered under the ADA, and because they are, you should tread carefully here. Under the Federal Fair Housing Act, landlords are required to make "reasonable accommodations" to allow a person with a disability to enjoy living at the premises. In your case, allowing the therapy dog to live on the premises with a doctor's note is a reasonable accommodation, even if it goes against your typical pet policy. It would be advisable for you to have an addendum to your lease with this tenant to specify what the rules will be for this service dog and how far you are willing to go to accommodate your tenant. I would recommend discussing this with an attorney in your area to determine the scope of that agreement. This will ensure that your needs and concerns are met with the dog without you getting into hot water with HUD or a civil suit from the tenant.