当用户刷新页面或导航到不同页面时，侧栏上的广告不同

I have a sidebar with a section for an ad. I want to display a different ad on that section when the user navigates to a different page or refreshes the page. I want to rotate about 5-10 ads. Each ad is a script therefore having more than 10 ads will slow down my page. What is the best way to rotate ads on refresh or when a user navigates to a different page? It is for my wordpress blog but I prefer not to use plugins. I have a sidebar with a section for an ad. I wa