4 ft. x 100 ft. Landscape Fabric

Yes

I've used this kind of product for over 30 years. Perhaps if you lay concrete over it with no seams in the concrete you'll never see a weed! But if you lay rock on it, over time, blown in dust will accumulate between the rocks creating soil that small weeds can take root in. Even when you use tightly spaced pavers or brick over it, eventually smaller weeds will find a way to get into the seams. This kind of barrier material does make it hard for roots of any kind to penetrate it from below, and while very effective in the short term, was only invented in the last century or two and is facing an enemy that has evolved over billions of years. If you use it with rock then expect to have to maintain it by screening your rock every 5 to 10 years to remove the blown-in soil in which roots can take root. I built a box with a 1/4" screen bottom that fits over a wheelbarrow that I shovel the rock into that lets the loose soil fall through and then return the rock. For brickwork or pavers you may have to dig out small weeds after a few years using a putty knife. In that sense, a cleanup every 5 to 10 years, is not too high a price to pay. The product is good and a bit easier to work with than the grey cloth that is more like stiff paper. Both work but there is no perfect solution against weed infiltration - they've trained a long time! And keep in mind that weeds generally attack from above so if you use this as a barrier between two soils, you're enemy is parachuting in, not tunneling!

I generally overlap by 6" or so and staple it in the middle of the overlap. And I think you already know the answer on river rock - blown-in dust carried on the wind will eventually create a fertile soil for weeds. So every 5 to 10 years I've had to make a pass through screening my rock to remove the built-up soil. I fabricated a wooden box with a 1/4" square mesh metal screen on the bottom to fit over my garden wheelbarrow to shovel the rocks into and let the accumulated soil fall through. It's tedious but you don't have to do it every year, only something like 5 to 10 or more years depending on how windy your area is. The finer the rock the less likely the blown-in soil will create a fertile opportunity for weeds - but eventually it will. But the finer rock is harder to screen since it will fall through the mesh of the screen. As you can see in the photo I have a mix of pea gravel for walkways (reinforced by a fine gray sand so you can run a wheelbarrow over it) along with mulch and rocks for ground cover. I also have some walkways with 16" square pavers and 1 to 2" river rock as accent filler. I think I prefer the 1 to 2" river rock as it is the easiest to cycle through the screening process.

You can remove the weed before placing it, but as soon as you will staple it to the ground so no sun coming through it will dyi.