You actually park your car in your garage?
I use my garage as a woodworking shop, or as a project center, so we rarely pull a car in unless I need to work on it. I've never had an issue just pulling in and eyeballing my position. But we have small cars and a 28' deep garage (about 24' if I don't count the attic stairs).
I would much rather have the traditional tennis ball on a string touching the windshield, or one of those fancy laser markers to indicate my parking spot. My mom hung a small stuffed animal in her garage and knew she was in the right spot when it smacked her windshield.
I wouldn't want an obstacle on my garage floor. It would be a tripping hazard and would get in the way rolling my tools around the garage. I also wouldn't want to put adhesive, or screws, or anything that might damage the garage floor for future use (if I want to epoxy coat or something).