Try to avoid creating blind spots on the shop floor. Remove obstructions or reposition merchandise that may prevent staff having a clear view around the shop, the entrance and, if possible, outside your premises. 

If you still have blind spots, is there anything you can do to improve these areas, such as repositioning a CCTV camera to cover it? Alternatively, can you temporarily seal the area off from the public?

Adding security mirrors will enable staff to have more visibility around the store and may reduce blind spots. Ask staff to pay extra attention to areas of the shop you have identified as vulnerable, especially where high value or attractive stock is displayed. Alternatively, move the stock to another location, or reduce what is on open display. 

Never attempt to lock a shoplifter in the shop. This is dangerous. Call the police.