Gardening and Landscaping DesignGarden Ideas for Planting & Design

We have several very large beds with both bushes and perennials. When we put them in a few years ago, we carefully put down good quality landscape fabric and lots of mulch. It was formerly a grassy area, so we did it thoroughly and overlapped the fabric quite a bit the first time to help inhibit grass & weeds.
I add in lots of fresh mulch every other year.
It just doesn't keep the weeds and clumps of grass from poking through.
What product can I use (spray?) on the weeds or liberally around the beds that will not hurt the plants and flowers?
Please suggest something readily available at Home Depot & Lowe's type places.
Thanks!!!