Solid credit, but it's reducing with each deal

[Luke M.]

I started out with a credit score of 790 when I bought my first rental. In 3 years, I've acquired 4 more, and my credit has dipped with each loan, and is now at 710. I have no debt except for these loans, and no credit card balance except for what what is used and paid off each month. Does anyone have any tips or strategies for how to boost and maintain my credit score in order to get me to 10 rentals? I could pay them down, but I'd rather keep the loans as I don't think I'll be able to get money that cheaply in the future.