You don't mention what sort of weeds and the site you you want to clear but from my experience (with couch grass as main problem) the black fabric sold in garden centres is too thin to be a permanent suppressor. The grass can grow in a weaker fashion under the fabric and can sometimes grow through it. Perhaps double it up or put wood chippings on top as well? Elsewhere I'm using thick black plastic for covering large areas and I'm leaving that down for a year. In other sloped areas I'm using newspaper covered by cardboard , held down with stones. Depends on whether you want it to look tidy or to be effective!

I have a real nettle problem in our new garden, (the last tenants never cut the grass for more than five years!) I have used that weed membrane Rozalia spoke about but I have layered all the grass that I cut down on top. As Rozalia says it's a case of looking good now or in a years time!