Question
i have a dog that is tied at the base of a big oak tree in ohio, she likes to dig to get cool dirt to lay in.   will this hurt the tree, she digs right at the base and my wife is afraid she will weeken the roots that it may fall on the house.   the tree is about 60 to 70 feet hight and about 4 to 5 feet around

Answer
No it is not going to hurt the tree or weaken the root system. Most of the roots are with in the spread of the branches and with this large of a tree the root system will be very large and spread out so the digging by the dog around the tree will not harm the tree.