A decade ago, my mother had her place "professionally" landscaped, they put black plastic all over the place to keep down weeds, then put mulch on top. It looked good, for a couple months, but every weed seed that landed on top of the mulch grew. The black plastic only prevents weeds that are already there from coming through.
Because my mom wasn't a diligent weeder, the place was soon just as infested with weeds as before the plastic was laid down, but the problem was worse, because the roots grew through the plastic and into the ground underneath, anchoring it there.
In some places, the plastic was that "mesh" with tiny holes in it, and other places it was solid. If you aren't diligent about removing every weed that sprouts, you will have this problem, then you also have the problem of being unable to remove the plastic when you want to change the landscaping.
Corrugated cardboard (especially refrigerator boxes) is an excellent weed barrier, but you can use newspapers too, laying it very thick (at least ten layers, overlapping the edges).
For weed prevention, use "corn gluten meal" which prevents weed seeds from germinating. You can get it at nurseries (Preen is one, but there are two types of Preen, read the label for the one that is made with corn gluten meal) but you can get it cheaper at feed stores like Agway. Apply the corm gluten meal in early spring and every few weeks throughout the growing season.
