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.
Step 1: The garbage
Cut the rounded part with the scissors and refine the border with a cutter, beware to not cut yourself! You'll obtain a boat shape, leave some plastic on the corners of the back sides, so that they will help to reinforce the connection with the frame.
Step 2: The hole
Step 3: The connection
The first solution, probably the simpler to find, is to use a spider nut of the type you need to insert into the fork pipe to tighten the handlebar on it. This time simply insert it from the bottom in the fork tube. This solution could be anyway unsuitable when you'll need to remove two spider nuts from the tube, one from the upper side and one from the bottom side, both oriented reversed referring to the extraction direction.
Step 4: An alternative
At the extremities of the elastomer the two washers will squeeze the rubber material so that it will enlarge in the central diameter locking the fender in place.
Step 5: Ready to ride!
When you mount the front half of the fender you have to check there are no interference between it and the fork arch, this depends on fork excursion, and you have to push down the fork at his maximum compression.
Obviously you can whenever add a second identical half-fender on the other side, mounted over the first one with overlapped holes, so to have a complete and cool protection against spurts.