Ditto routing the cable over the wheel nut. Don't know if you have a cassette or freewheel, but in any case, you'll need the requisite tool(s) to remove it if you're going to replace the spoke guard. While I agree that spoke guards are unnecessary in a well-adjusted bike, they don't do much harm. Luckily Amazon has a good return policy! At some point, you'll likely be replacing the cassette/freewheel - the teeth are showing significant wear, so the chain is likely equally worn. You'll need to replace both at some point, but if it's shifting OK now, keep using it, while recognizing that there's a drivetrain overhaul on the horizon.