In these parts Double Check Valves are pretty much the standard backflow device on 99% of the residential irrigation systems that have been installed by a contractor. There are specific reasons why Double Checks are preferred in our area. And if someone really wants to know - just ask. Otherwise, I was just curious what the rest of you all used. For those in warmer climates, I assume you use some sort of above-ground backflow device like a AVB, PVB, or AS Valves. But those seem so tacky - to have these big things sticking up in the air along side someone's house. And for those in the cooler climates where it freezes deep (e.g. Colorado, Dakotas, Montana, etc.) I would think you'd use a double-check as well because of the fact that it's underground and at least somewhat protected from the freezing.