Usually mountain bike fenders
, particularly on suspended forks, are connected to the steering tube of the frame. They're one or two plastic pieces, more tough at the connection side, to resist at a good flexible force.
In this instructable you'll see how much easy is to build your own bike fender with reused plastic stuff. This is not only fun and cheap, but it also will convert at once a garbage into a plastic gadget ready to use, and this is the best way to recycle.