We always used hay bails. stack them three wideand four tall in a teated wood frame with a tarp covering them. They last a couple of seasons and then became multch for the garden and trees.
My brother tried stacking cardboard so you could shoot "on edge" but it wasn't as good as the hay and was harder to get rid of. I don't have the room to shoot bow in my yard anymore so I haven't done it in years.
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BMW M3 HISTORY