This would be used certain areas to block you from going past it. It could be called substitute, and if you interact with it, it will pick it up. It'll only block you, and won't effect anybody else around you. I'd imagine it would be easy to obtain. Perhaps make it somewhat late game?
If you look at the image I posted - you simply place it down and it won't allow you to pass it, potentially saving lure encounter steps or making farming easier for some people.
Let me know what you guys think of this idea!