Got some Structube Maxwell chairs with the tube metal chair legs that the robotic vacuum struggles on, since it cannot see them with the lidar and they are too low for the bumpers so it constantly tries to drive over them and get stuck or make a bunch of noise.

Made this boundry piece that clips into the legs with no hardware or glue, the project file has it already cut into 3 pieces with dovetail connectors, just clip the piece on either side in and then slide the middle piece down between them, might need to spread the side pieces with a bit of force as they are pretty tight but it fits snuggly once you push it down. Each chair requires 2 of these, one for each leg.

printed with 5% infill and it's solid enough for the purpose, just don't kick it or pull on it with too much force.