Finding Shelf Labels

I'm re-opening a local grocery store and am in need of label advice:

-I don't want the electronic labels - it's a small enough store that changing tags won't be a problem.

-The shelf face is approximately 4" tall (I know, GIGANTIC, but it's the shelving I'm working with) - I'd like to find either realllllly strong magnetic labels or the plastic sleeve that slides into the grooves so stickers aren't going directly onto the shelf but onto the magnet/sleeve, something that can't easily be knocked off or switched around by the roving tweenage bike gangs or crabby old farmers who think they know best.

I still have some time before opening day to get the label arrangement figured out, so any help is appreciated!