If they are legitimate service animals you cannot legally keep them out, nor should you want to.
Of course there's always the chance of something like this happening:
Snake brought into restaurant rattles nerves
I just now viewed the link you posted. That is happening almost everywhere. If someone came into my church, I would be going out the back door, and I'm sure others would follow.
This event shows the need for the ADA to inform the public, and business owners as to what a service animal is and is not. What makes it difficult, and contributes to the abuse of true service animal status, is that a business owner is not allowed by law to question, ask, or require proof that an animal is truly a legal service animal. There are some states that are now beginning to fine people who abuse the ADA laws pertaining to service animals. Thanks for posting this.