The idea is not new but until now I have not seen one bike with such a mud- guard/flap.
please do not wonder about the three different bikes in this project. The green one has the fist prototype installed to test the approach. The one shown in the step here is the second approach which looks much nicer. Then the last one is the secondary bike of a god friend of mine. At this point thank you T.K. for all the pictures and additional information.

I'm now using the Mud-flap for one year ans it is great. The only thing to consider is to clean your fork from time to time. A lot more dirt is accumulating on the critical parts.

Supplies

Hammer
Coffee
punching iron
ruler
punch holes
zip-ties
old inner tube

Step 1: All About the Size

Measure the gap of your fork. Here it is 70mm or 2,75 eagle units. We will double up the tube for a better fit of the punch holes but also we will shorten the tube for a better look and nothing wobbles around.

(70mm-10mm)*2 = 120mm

or in more general:

(x - 10mm)*2

x is the measured distance.

Step 2: Prepare the Tube for the Punch Holes

use a punching iron to cut the holes for the punch holes. These need to be somewhere in the 4 corners. Leave enough distance to the corners!

Step 3: Add the Puch Holes

Well, read the instructions on the package or have a look at the photos... there is no magic

Step 4: Zip-tie It to the Fork

use 4 Zip-ties to hold it in place.

One general tip, always carry some zip-ties with you. these little things are so useful and durable. Half of my car is held together with zip-ties

Step 5: How Does It Look Like After ~1year

As mentioned I'm using the mud-flap now for one year and it is simply great. On that approach we have not used the punch holes... it was meant as a quick test but now I'm to lazy to change it. The idea with the punch holes are from my friend T.K. it looks better. We cant tell anything about the durability, we both are using it until now and both solutions are still without any tear.