You also indicate that with all this food around, it is a challenge for dogs to remain under the table, that they get bored and only wait for an opportunity to start a fight.
Because I am a firm believer that American dogs are no different from their European counterparts, I wonder why this should be the case here in the United States when it never happens in Europe. Of course I had witnessed dogs growling at each other in Viennese cafes and Berlin restaurants and Parisian bistros, so what? If the person accompanying the dog is in full control -- as every such responsible person should be -- nothing ever happens, the dogs get calmed down and all is well. I traveled with big dogs all across Europe and took them to every imaginable public space without incurring any problems or difficulties at all.
I am always sad to see people leaving dogs in their cars in the United States -- even in the heat of the summer -- or at home for many hours all by themselves, often in confined kennels, simply because people cannot take dogs to restaurants and public spaces.
As a dog trainer, you should be encouraging people to take their dog wherever they can and have them sit in cafes when the weather is beautiful and outdoor life is blossoming in a lovely town like Ann Arbor.