Slander

I have a competing business owner that has been reporting false information about my business to customers. These customers are usually foreigners and are in town for only a few days. They have agreed to write a statement about the statements made by the other competitor. The statements are about the pricing of products and the handling of money transfers. My question is: what legal forms can I have these foreign customers sign? and Will these forms stand up in court since they are from another country and they can't be present in court? There is a loss of business due to these false statements, but I can't put an exact number because it's more of a loss opportinity. I'm in VA. Thanks