How to support 4x4 posts on cement driveway
+1 option #4, plastic standoffs.
&quot;Any thoughts on the most robust way to anchor the posts?&quot;
You said you are renting and can not anchor.
Take some five gallon buckets and mix up some cement, fill the buckets with the cement and put an eye bolt in so it stick out of the top. Put a nut and washer on the threaded part of the eye bolt  that will be in the concrete to prevent it from being pulled out.  Now you can place these on the sides of the structure and use rope or ratchet straps to secure the structure down to protect the wind from taking it for a sail.