Yeah, I've watched old timers place shiny materials underneath plants (can't remember what this deters), around vulnerable stems (think squash vine borer), and hung on strings at varying height near plants. Some bugs hate the bright light, others hate the movement, and others are afraid of their own reflection. CD's I think would have a tendency to constrict the plant if it were to grow through the hole, but you could use halves. (I'm assuming these CDs aren't important to you in any way.) Your only risk is that you might lose wayward CDs in the soil, and sunlight does begin to break down plastics which could then leach into the soil. Aluminum foil and Mylar work, too.