MILITARY LOW FLYING TITBIT......
Many moons ago my Jet Provost QFI, who was by then a "mature" Flight Lieutenant with a great sense of self-preservation
, taught me to maintain 250' MSD (min seperation distance) by telling his students "cows have legs but sheep don't!"
That is to say if you could see the legs on a sheep you were too low and if you couldn't see legs on a cow as you flew past you were too high!
I don't know if this is a universal part of the QFI "patter" but it worked for me.......
MB