I have my own SEO clints who are getting monthly basis SEO services from me, some time when i'm going to charge the cost end of month some of them skip the do payment. What we can do for them continue to SEO each month. because once client see the keyword comes first page they happy with that result and try avoid the continue SEO. then it is a huge loss for my site, becuase i'm getting client to contiune at least 1 year for SEO. Any suggestions? Appriciate your ideas. Thanks.