How can one remove the ability to place bedrock?

Ok this might not be the best answer but I was thinking of running a command 20 ticks a second.

/execute @p ~ ~ ~ /fill ~7 ~7 ~7 ~-7 ~-7 ~-7 air 0 replace bedrock

This would work but it would also delete bedrock that the player has not placed i.e naturally spawned in bedrock.

Another method that I was thinking was to set the player in Gamemode 2 whenever he is holding bedrock in his hand, for example:

/testfor @p {SelectedItemSlot:(changable),Inventory:[{Slot:(changable)b,­id:"minecraft:bedrock"}]­}

Then make that flow into a command block that makes the player in adventure mode then a redstone torch that changes the player back into the original mode.

Hope it helped