Cotoneaster Horizontalis removal
Years ago my grandfather put this into his garden for some reason and since then it's grown beyond control, taking over fences and growing out into a snicket and making it difficult to walk down. He passed away and my grandma can't keep upto it so we're looking to remove it, I dug down a few inches but the roots have grown deep, wide and thick. What is the best method of removing this pest, Am I forced to remove it or can I use some form of pesticide to get rid of it?
For the record it's this horrid thing: