Staples?!? The best thing about asking a Home Depot worker how something should be done is that although the advice is not often right, it often quite amusing.

I used an extra-strong, extra sticky duct tape. It worked well for connecting the pieces together, although I haven't yet found a good method for attaching the plastic to the concrete block walls. I had the pieces of plastic overlap each other by about 18" along the seam area.

Tape and a plastic compatible glue on the lap joint. Be sure to run the barrier up the stem walls and seal it there as well.