How to Remove “Collar Ring” Stains from a Custom Shirt?

I have a client that asked a question concerning care of his custom shirts. Is there anything to help prevent “ring around the collar”? or at least slow it down.
We live in the Southern States and is constantly warm and humid. Shirts have to be cleaned more because of that, especially shirts that are light, they seem to collect dirt around the collar.
Any thoughts, besides cleaning the shirts more often?