Do not arrange to meet them at the finish line. It’s not a meeting place. It’s a human mosh pit. Everyone is crying, hugging, or lying on the ground. Trying to find your runner there is like trying to find a specific grain of sand on a beach.
Instead, pick a post-race letter on the barriers. The marathon uses letters A through Z for family meeting points. Choose “M” for “Meltdown” or “P” for “Pub.” When they text you “I’m at K,” you walk to K. It’s surprisingly effective, even when your phone battery is at 2%.