Can I make pistons retriggerable?
Solution 1:
There is a way you can detect if a block is missing using a repeater and redstone current.
The further stone-block is destroyed in between the images. As far as I know, this is the only way to do it without clocks (pulses). The piston itself does not keep itself triggered, but that can be implemented with memory cells if need be (See 3rd image).
