What works is the elastic at the bottom its easy to pull down and fits snugly into place.
What doesnt work is that theres no way to hold the middle bit in between the back of the couch and the seat cushions, or between the arms and the seat cushions, so its VERY apparent that its a basic cover, as it quickly forms a flat diagonal from the top of the couch to the front of the seat cushions.  I have no clue what the technical fix would be for that, but it was be amazing if there is one!