but doing so to a flash-memory device could destroy it due to its limited number of write cycles.
Well you will at least need to write it once to erase your data although 7 pass is recommended:
Try the following as root (where XX
is where your flash card is "ex: sdb1")
dd if=/dev/urandom of=/dev/sdXX
and when they say "limited number of write cycles
" it is in thousand or even million times, so it's not this few pass that will put your memory flash into the grave