As it turns out? It's damn easy to sneak up on Strange. He's sitting in front of the lake, deep in thought, not really looking at anything. A family of Loch Ness Monsters frolic in a way that would be absolutely adorable if Strange was paying them the slightest bit of attention. But he's lost in thought, looking vaguely off to the edge of the lake as he thinks about something.

Occasionally he's making scratches in the earth with a stick. It looks vaguely like a football plan, with lots of x's and a large o. But there's also a few spirals and stars, like Strange was doing the drawing in the dirt equivalent of doodling.

Unless 9S completely bungles his stealth, it's pretty easy to sneak up on him.