Ahummm if I was really worried about 100 pounds falling 30 feet and landing on my sitting position, I bet your sweet posturer, that old da would have a factory built and PE certified canopy,,lol..
Though I will add this, I have had the un-pleasurable task of investigating more than one fatality, due to faulty ROPS and cages that have not been certified by a PE.
If you are working under heavy objects that may fall, please don't do/ build something that you may place unjustified faith in, and have it fail. I know I'm singing to the boys in the band here, but I have seen to many things go wrong at the wrong time with sometimes fatal results.