Removing invaders is a pain. We are trying to reduce the brambles and briars in our top paddock (with a mix of spraying and brush-cutting. Slowly slowly: it seems to take 4 or 5 treatments over about 3 years to really fix them. Then we have all the annual weeds from our neighbours that blow in (or float in when the Creek floods) and seed!
My sympathies. We feel your pain, as they say. In addition to the Norway Maples, we have a plant called Japanese Knotweed that we have been fighting. It creeps in whenever a tree is taken down. It is incredibly invasive. What we are trying to do is to overwhelm the Knotweed with native plants, mostly bushes, grasses, evergreen shrubs including native azaleas and evergreen trees and to also increase the shade cover across the yard since the invasives do not seem to like shade as much as they like sun.