I've frequently landing in the grass alongside paved runways. One of these, as I was rolling out, I saw surveyor's flags flicking past on both sides. When I got to the fuel pump, I told the airport manager of this small rural field, "Nice grass runway."
He said, "Thanks - I just put it in today. I'll be closing the pavement tomorrow with a Notam for repaving."
The flags were totally invisible until I was on the ground. Good thing I didn't run them down, just pure luck.
At another field, there was a bunch of junk on the side I preferred, so I landed on the rougher and shorter side. After refueling I strolled out to see what the junk was. Turns out it was runway markers, homemade ones that sure weren't recognizable from the air.
Dave