Mary Louise and Marty showed up faithfully at the park each morning at 7:30. Stopping their SUV in the same space, Mary Louise, 68, emerged with a bowl of water, followed by her husband, 85, and armed with a tennis ball. They opened the car’s hatch as if they were pulling back a Broadway curtain to reveal the show’s marquee star.

Shamus, their 3-year-old border collie, played the role well.