I have seen some kennel sprays that are supposed to kill it and I have heard bleach as well but if it is in the ground I don't understand (or believe) you could saturate the grass enough to penetrate the dirt really well.
Do you have parvo on that part of the yard?
I've only had this kennel setup in this location for about a year & this is my first set of pups to attempt to raise on them... I'm gonna call my Vet too But I usually ask ETHD first, lol....