The acreage we seek is in a hilly place, and I forsee having these problems. That's a great idea, Slingha!
Terracing is another.
I saw once on DIY network where the landscaper dug two holes on the hill. He planted the tree in the forward hole, used part of the dirt from the back hole to raise the dirt in front of the tree, and when it rained, the back hole would fill with water, aiding in watering the tree, and the dirt in front would divert run-off down the hill. Hope that makes sense. Maybe you had to see it........ Everything looks easy on TV!
Suzi