Use old rug runners around where you don't want the weeds to grow through, and put mulch over it. It works great! No weeds grow through that. I use them around my house, where I just wanted certain plants to grow.
Source: I thought of this myself, I was sick of all the tips I read that didn't work.
Very good idea is plastic bags or any kind of plastic will do the same. Thanks for sharing, here's picture of my small raised garden. I put down plastic then made the garden, good luck.