About 2 years ago I had a tree removed from my front yard and the stump ground. I was told that this was enough to kill the remaining roots. However, I don't believe that this is true since the driveway is cracking and splitting even more now than when we had the tree. One side of the crack is about 3 inches higher than the other and continuing to get higher. Also the walkway is slanted to one side. How can I take care of this problem? Is there a tree root killer that I can use at this late date? Thanks for any help you can offer!