Cabbage white butterflies are antisocial when they're laying their eggs. So if you stick up decoy butterflies, you can scare them off your crops. It's slightly oversize so it looks more intimidating to butterflies. Feel free to evolve the design.
Ignore butterflies attempting to mate with your decoy. They are stupid males and will not be laying eggs.
Print in white (or spray) and melt/glue a piece of filament into the socket on the underside of the butterfly. Warm up a strip down the middle of the "body" and bend the wings up a bit into what aeronautical types call a dihedral.
Draw a black spot in the middle of each of the two smaller wing lobes with permanent marker, and plant so that it is visible above your crops. Relax in a caterpillar-free environment.