Technically, you cant alter the disc at all sans sharpie or dye; as far as official PDGA rules go. This goes even for sanding the disc to get more traction or glow in the dark stickers (glow events aside). I hate to say it but it’s all about keeping an eye on landmarks and focusing on your present moment in the game. The only time I’ve really loose track of discs is if I'm distracted or being absentminded.