Middle Son has a service dog, Willow, who we've had for about a year now. Middle Son is a wanderer. Given the opportunity he will slip out unlocked doors, open windows, or climb over fences. Any time he goes outside, I strap the dog to his belt. It's very difficult for a 12 year old to climb over a fence with a 90 pound dog strapped to his waist.
Yesterday we went to the grocery store. It was me, Youngest Son, Middle Son, and Willow. I forgot to put Middle Son's belt on, so I had him hold the leash. It seemed like he and Willow had a lot more trouble than usual. Willow was distracted and looking at other things, Middle Son kept pulling in different directions, etc.
We went to the grocery store again tonight. This time I made sure I had the belt. They both seemed much more focused and calm.
Both dogs and children with autism are driven by routines. Sticking to the familiar script makes them both more successful.