There are a variety of aftermarket chain guards out there. Many mount using some type of tube clamp. The OEM (Orignal Equipment Manufacture) quite often are mounted using a welded or brazed on bracket. Getting one to clear the derailleurs and chain as it moves across the cogs and rings. I have one derailleur bike that has a chain guard, that guard was mounted on tabs welded on the frame. The guard itself was plastic and has since broken and will be replaced by an aluminum one when I get around to making it.
Aaron
