This machine will clone the block that's coordinates you entered; and randomly place it under a ArmorStand named spot.
This Video explains most of it!

https://youtu.be/UKv1JoIe_8M

Commands:
SetBlock clock commands:
/setblock ~ ~1 ~ wool
/setblock ~ ~-1 ~ redstone_block

To get Armor Stands:
/summon ArmorStand ~ ~ ~ {CustomName:"here",CustomNameVisible:1,Small:1}
/summon ArmorStand ~ ~ ~ {CustomName:"spot",NoGravity:1,Invisible:1}
/execute @r[type=ArmorStand,name=red] ~ ~ ~ /setblock ~ ~ ~ redstone_block

And for each Block you want to randomly place around:
/execute @r[type=ArmorStand,name=spot] ~ ~-5 ~ detect ~ ~ ~ air 0 /clone [the coordnates of the block do this twice] ~ ~ ~ replace air

Also if you want to have it constantly execute use this to reset it:
/setblock ~ ~ ~1 air