I leveled my yard with fill dirt and covered with screened 1/4 rock. No barrier.
I used an insecticide to eliminate any ant/bug problem in my fill dirt.
Applied weed impede as directed and watered it in with round-up.
It has lasted exactly one year.
Bought first bottle recommended from nursery in Tempe, Az.
Getting ready to apply again.
Excellent product as long as you use it every 6 months as directed (in AZ that is in March and October). Be sure to water the applied area if it des not rain. I have 1.25 acres with almost no weeds when used as compared to my neighbors that have weeds all over. I am a life long user now!