I find far less robbing when I feed in the open, feeding all colonies at once, summer or fall. There is no incentive for the bees to go to other colonies as there is no more syrup there than at home. A leaking hive feeder is the worst for promoting robbing. My bees pay no attention to people in the yard as they are busy collecting syrup, just as they pay no attention when collecting nectar on a flow. When all colonies are fed, all of the bees have an incentive to stay home and guard the hive instead of robbing, just like a flow. I feed out of direct site of the hives, about 100-150 yards away.