"Emotional Support" dog in Texas

[Stephen Hayworth]

We have some tenants who, after moving into one of our apartments, declared that they had acquired an emotional support dog. We have asked them repeatedly for documentation and they have not complied. They emailed us the certificate that anyone can print off for $25 online, we told them that wasn't sufficient and that they would need a note from a licensed mental health professional, and they have not provided it. 

Then I found out that the dog is spending its days tied to the front porch, and I've now gotten 2 complaints in the last week about it. I'd like to get the dog either removed, or tell them they have to keep it inside, but I'm really unsure what kind of legal ground that puts us on. Anybody have any helpful advice?

LEASE NOTE: We've done a lot of single-family, but this is our first multi-family venture, and we didn't realize that we really needed to use a specific multi-family lease. So the lease doesn't really specify anything about 'common areas' and what is or is not allowed.