Just get some sandblasting resist ( glass art supply ) and sandblast it in. It’s like thick plastic film, it’s rubbery, resists being abraded. You can do very nice details with it. Fast and easy. You could even laser cut the template. Whole job should be an hour or two, plus finding a rock. I envisioned it cemented halfway into the sidewalk, just enough to trip on. Maybe that’s just me…