Something like this could be used for high dollar items. While it may block part of the card when put on, it could be removed for the right customer. If someone tries to cut the wires without disengaging the alarm, it will continually sound off. Not the best solution, but the appearance of antitheft devices would be a deterrent within itself.
https://www.ebay.com/itm/Alpha-Alarm...gAAOSwYUdbM-PZ