Here's what I would do.

Get a billboard done up and sit in the parking lot on public property in front of the store every Saturday. Hand out flyers to people who seem like they might be headed into the store.

Eventually you'll cost them enough business that they'll have to silence you.

Make sure you keep it true though. Use a bull horn too!!! If it's warm out, make it a party and give out free lemonade!!!

Had an experience like this out front of a car dealership years ago over a few hundred bucks.

100% effective