: Place a Sponge or Yellow Wool on top of the Observer.

This method is perfect for Survival mode as it uses basic Redstone components to trigger a surprise when a block is broken. : Dig a 3x3 hole that is 3 blocks deep.

: Place a Dispenser (or a Dropper ) directly underneath the Observer.

: Place an Observer in the center at ground level with its "face" looking up.