Is this what I need? I can clip/prune/lop intrusive seedling(!) trees
and whatnot, but I keep stepping on 2" tall stubs (and the devils keep
sprouting from the 'stump'). Should I invest in a mattock (or some
other digging tool) to whack these suckers slightly below-ground? I
really don't have the energy or strength to dig up the entire root
mass. And at this point, creating divots in my back yard "lawn" is the
least of my worries.

If a mattock seems appropriate, any recommendations for something
sturdy enough to do the job? I've just looked at a couple of web sites
and see a 36", 5lb gadget (TrueTemper). I think, perhaps, something
with a longer handle and more weight might require less total effort.