Take a look at the Rain Bird AntiSiphon Valve.

Available Here: https://sprinklersupplystore.com/page...

AntiSiphon valves are installed above ground and will prevent backflow if properly installed. AntiSiphon valves should always be installed at least 6" above the highest head on the valve line, and should never have another valve installed further down the line from the main valve. Rain Bird AntiSiphon valves also feature our patented vacuum breaker–available for automatic or manual applications. All Rain Bird AntiSiphon valves work with any standard sprinkler timer.