What are you trying to load with 500 amps?Correction, not mosfet, thryistor.
I found this:
https://en.wikibooks.org/wiki/Practical_Electronics/Crowbar_circuit
It seems to be ok, and also protect from AC.
Im thinking about using my dl with up to about 500A, of course within SOA.
There may be better ways for that much current.