The best way to unsort an array? Sort it!!
@a=0..20;$,=" ";
print sort {1-int rand 3} @a;
OK, I couldn't resist golfing it.
Actually this is a really bad randomizer. It behaves more like an incomplete shuffle. It's also not guaranteed to finish but the failure should be extremely rare.
s//----->\t/;$~="JAPH";s//\r<$~~/;{s|~$~-|-~$~|||s
|-$~~|$~~-|||s,<$~~,<~$~,,s,~$~>,$~~>,,
$|=1,select$,,$,,$,,1e-1;print;redo}