When redstone powered a sticky piston when the sticky piston has a block on the end of it, the pistons activate when the redstone is powered, but when the power to the redstone is turned off, the pistons retract then the redstone dust going to the repeaters to the pistons pops off of the block and can be picked up again.

Video showing here: https://www.youtube.com/watch?v=NNudMurTj9I&feature=youtu.be