The following suggestions can be used to keep bats away before they become pests.
There are no chemicals registered in Minnesota for use on bats. At one time DDT and Rozol were used to poison bats. However, these chemicals could seep into humans living quarters posing a significant health hazard to people. Use of these chemicals also greatly increased the risk of humans and pets coming into contact with sick or dying bats. Their use has been discontinued and is now illegal.
The reason most methods of bat control fail is because they do not prevent bats from reentering the structure. Whether tackling the problem yourself, or hiring a pest control operator or carpenter, the goal should be the same - non-lethal, non-chemical, permanent, physical exclusion of the bats.