[Delphinus]

I've run both anti siphon holes and check valves on tanks in the past. Both are methods equally prone to failure and there will always be a chance they fail one time when you're unprepared. Maintenance will reduce the risk but not eliminate it completely.

I prefer the KISS principle.. On my tanks I run now I keep enough space in my sump to handle the backflow. The higher the output nozzles the less backflow volume you need to account for. Plus, having output nozzles near the surface has the added advantage keeps better surface agitation.