Right now I'm doing rust repair at the bottom of the car, and I don't have a lift. That means sitting cross legged on the ground, with the car on jackstands. To keep the sparks off, I use cardboard. I'll sit on the edge, and draw it up over my knees, and tuck it up under my arms. Then the sparks just roll off and hit the ground. Note: don't rest your elbows on the cardboard, cause sparks will get your elbows.