You may want to quit trying. Mulch these areas or plant ground covers. Trees do not have a nervous system, but they do know when they are hurt. Within seconds of damage, a tree is alerted and begins to take action. To do this best, they need several things.
Water is most important.
Wet the soil to a depth of 12 to 18 inches during dry periods. Soaker hoses are good for this. Let the soil dry well between waterings. This will often mean waiting one to several weeks before watering again. Remove dead limbs and mulch around trees.