Here are details on a full length mud flap I made for my Discovery to protect my Tvan from rocks being thrown out the back.
DescriptionThe mud flap hangs from the vehicle tie down points on either side of the fuel tank. I used the 400mm wide belt as I have a roughly 50mm lift, if you have a standard height Disco then the 300mm belt may suit you better.
I made the length of the mud flap 1800mm which brings it out of the side of the car to match the existing factory fitted mud flaps. You can cut yours to suit your requirements.
Parts:1 x 25mmx25mmx2mmx1800mm galvanised RHS (local metal supplier)
2 x 25mmx25mm plastic plugs (local metal supplier)
2 x Shackles (Bunnings)
20 x tek screws (Bunnnings)
20 x mud flap washers (Bunnings)
1 x 3 ply 6mmx400mmx1800mm rubber belt (Clarks Rubber)
Total cost was about $90.
Method1) Determine the lenght you require your mud flap to be.
2) Cut RHS to desired length.
3) Find the middle of the RHS.
4) Measure 390mm out from the middle to both sides and mark.
5) Place RHS under vehicle and ensure marks correspond to tie down points.
6) Weld shackles to RHS. Cleanup and regalvanise.
7) Attach belt to RHS using tek screws every 100mm. I placed the RHS 30mm from the top of the belt.
Photos
Mud flap attached to the car.

Close up of the shackle hanging from the tie down point.

Mud flap off the car.

Closer shot of shackle and dimensions.
Andrew