My first year using chop and drop and still learning. I did recently see a bit on "Gardening Australia" about chop and drop - don't drop the chopped bits around the plant you just chopped from. Move the chopped parts to another part of the garden. Does this address your concerns? My comfrey has been in the ground for years and grows in a lot of clay in mostly shade. It does travel a bit but not that much considering how long it's been there. I usually edit the plants during spring cleanup when the foliage looks ratty after winter. Seems to keep it in check here. I don't have quack grass so can't offer suggestions about it other than an impervious edging product. I have a small trench around a lot of my beds, bordering on fescue lawn and do have to clear the trench a couple of times during the growing season.
