Some things that make me feel more safe are keeping the jack in place, throwing some wheels under there, or placing an extra pair
of jackstands someplace out of the way.
Not exact matches
I would say never get under a car unless it's supported by something like a
jackstand, or a substantial chunk
of wood / metal / etc.
I'm redneck enough to accept a chunk
of creosote post or a piece
of an 8x8 beam or something instead
of a purpose built
jackstand, but don't trust just the jack alone.
Without getting fully under the car, pull / push on the
jackstands and make sure none
of them move.
Some point
of the frame is going to contact the
jackstand first, and its going to flex accordingly.
Our first order
of business was to get the front axle on
jackstands and accessible to disassemble the aged axle drum assemblies.