I have a very large red oak tree that lost a limb (15" diameter?) longer than 15 years ago. I've been told that it is probably rotten inside and should be taken down as it would be a threat to our home if it came down due to winds or?? Is there a way to determine if the tree trunk is bad? I thought about drilling a hole in towards the center of the tree and seeing if there is any softness as the bit penetrates the tree. The trunk diameter is probably 3-4 feet near its base. Any thoughts/suggestions? Thanks in advance