Using Reappearing Blocks
Reappearing Blocks and Reappearing Controllers are versatile tools which can be used from everything from doors to mob farms.
When a Controller, activated by redstone, is next to a Reappearing Block, that Reappearing Block transitions to the "on pulse" state. This pulse propagates through any face-connected group of Reappearing Blocks every 0.25 seconds (5 ticks), and turns them all transparent.
When in doubt, turn it on,
Similarly, a Controller that is not redstone active will turn transparent Reappearing Blocks back into their solid variant via an "off pulse" state.
and off again.
Remember that Controllers only produce pulses which propagate; they have no concept of the wider world, so to speak. This means that two Controllers connected to the same group of Reappearing Blocks will vy for control; if they have the same state, nothing will happen, but if they have different states, the group of Reappearing Blocks will pulse back and forth between the transparent and solid states.
They fight one way...
...and the other.
Since pulses act independently of the Controllers they came from, pulses can be trapped in a loop.
Blocks that are pushed into transparent Reappearing Blocks get broken.
To show you the power of Flex Seal,
I cut this Oak Wood in half!