If your going to use rubber roofing material for a "safety backstop" to stop any arrows that miss the target or pass though it then you may want to consider building a frame work to hang it from. Depending on how much time and effort your wanting to put into this project there are several options.
Is this going to be a permanent spot in the yard where you will always practice? If so and you are wanting to use the material you mentioned then here is one suggestion. Cut 3-4 pieces of the rubber roofing material the same size. The smallest I would recommend would be 4'x4'. Stack them on top of each other and use the same rubber roofing cement that they splice the material together with no less than 6" in all the way around the outer perimeter.
Next get a grommet kit and install them at the corners and approximately 1' apart around the outter edge and about 1" in from the edges. Next bury 2 - 4"x4" treated post leaving them 2' higher than the actual dimensions of the rubber and set them in place, use bagged quikcrete concrete in the holes. Span across the top whatever width you make the rubber +2'. Attach another 4x4 or 2x6 across the top to stabilize the structure.
At a hardware store you can purchase the other hardware needed. You will need eye lag screws to go into the wooden post and install starting 1' down from the top of the 4x4 post on each side and each additional point where you installed the grommets on the roofing material. At the hardware store also get some poly braid weather proof rope that you can weave back and forth from grommet to lag eye in a continuous length.
You would want a continuous length as it will loosen in the summer time as the warm rubber stretches and it may need re-tightened over time.
This may sound like a
to build but it is not as hard as it sounds.
I don't know what area you are from but I used old mine belting that we got from a demo job and attached it to the back wall of my back stop. I can tell you that arrow removal is difficult from this type of material if you miss your intended foam target or bag target. I would say the rubber roofing material will be difficult to pull an arrow from as well.
I built a permanent back stop 12' wide using all treated lumber last year and enclosed it in metal.
Perhaps overkill to most but I shoot a lot and have a lot of folks come over to shoot as well. When I find some more of the mine belting I intend to cover the entire back wall.
I installed a galvanized curtain track across the top and also installed a mesh curtain to keep the sun and elements off my targets when not in use.
