I like to ride my bike in my neighborhood but sometimes I ran into dogs. So I decided to carry my expandible baton. Since my bike is a 1997 it does not have disk brakes, but the fork is newer so it came with the holes to mount disk brakes. I decided to mount 1" PVC to where the caliper mounts to, and use it to carry my baton.
Cut PVC to desired length.
Drill holes to PVC. You will need two 10mm metric screws, 1/2" in length.
Mount PVC to fork (watch out and make sure the pipe clears the wheel spokes). I also installed a screw at the bottom of the PVC to stop the baton from expanding all the way down. This picture shows the baton expanded (screw not mounted yet).
Paint PVC with desired color. This is the final installation, the screw is mounted at the bottom of the PVC to stop the baton from expanding past the bottom of the PVC.
Now I can ride safely, and if I run into a dog, I can pull my baton and defend my self.
You could also carry other things in this PVC instead of a baton. Use end caps to keep your items secure.