Hello Bugman. I found this weird looking beetle in my dog’s water bowl and I promptly brought it into the house so that I could Google it. After not finding it, I remembered your site (which I’ve been to a couple times before) and searched through the pages of beetles but I haven’t found it yet. Its about the same size as a quarter (as the picture shows) and is a metallic green color with metallic copper color on the carapace (?). It sports a single curved horn on its head. Sorry about the quality of the pictures, its been gloomy and wet all day.
Your beetle is type of Dung Beetle commonly called a Rainbow Scarab, Phanaeus difformis. it is related to the similar looking, more common Rainbow Scarab, Phaneas vindex. BugGuide has a nice graphic that shows how to distinguish the two species based on the shape of pronotum.