Hard landings with my 3DR quad always puts it firmly 3 inches into the ground, splitting the legs up and destroying the nylon spacers.
I created these very simple bumpers so i don't have to dig up my quad anymore:
They are made from pipe insulation and a wooden hub from a broomstick i had laying around.
I cut up the stick in four 18 mm pieces to replace the nylon spacers and drilled a 3 mm hole in the center.
CA glued the hub to the middle of the foam piece and cut openings for the two legs.
Finally i replaced the two short 3 mm screws with a longer one that goes through both legs and the hub, securing it with a locknut.