We have a patio and realized last year that there are two trees coming up between the back wall and the cement patio. I chopped them but they were too strong to pull out by the roots. The chopping just made them happier this year. A week ago I poured Ortho Max week killer, a ton of it down between there to soak the roots and totally covered the part above it with foam from it. They're still growing. I don't know what type they are and am not familiar with what grows out here, but the bottoms are getting way too big and there's already a crack in the cement. Does anyone have any ideas on what I can do to kill them off? They refuse to DIE!