I am experimenting with growing either moss carpeting or moss walls, maybe both at some point. Here are my two test growers. The one on the left is moss sandwiched between 2 plastic grates (for crocheting I think) the one on the right is framed with the grates and then I used a mesh material capture the moss. Both are held together by stainless steel wire (thanks to my wife who took a jewelry making class). (I have also used small zip ties)

I think both will work fine for the purpose of growing the moss in place, I am more interested in the speed it grows and the patterns it grows into.