I have a piece of rebar hanging in the middle of the frame on my pickup. I run the sticks underneath hook them over the middle piece then use bungees or rope to tie to the bumper front and rear. I tie to the middle of the bumper on the rear which causes the bundle to bend. This assists in keeping the stock under MY truck.
so even if it gets loose you are only likely to puncture a tire.
Lest you think thats fine if you have a pickup, it was really fun to do the same thing in an 83 BMW 320i. The new hands at the steelyards are always amazed.