I finally gave up on card board, scrap wood and junk.
It never lasted and always left a mess in my yard.
I ended up buying 3 of these Poly Foam target backers from here:
http://www.letargets.com/estylez_ps.aspx?searchmode=category&searchcatcontext=~020000~020300
It was the BEST EVER small little investment I ever made when it comes to targets and pleasure shooting at home.
You can literally shoot "THOUSANDS-plus" of rounds through these things...just like the advertisement says...and they still keep on working. No lie. They are fantastic!
I took a couple of scraps....4x4 and 2x4 and a couple wood dowels and built my own stands for them for free out of junk I had laying around the barn.
You don't have to paint them, but I did just so the wood would last a little longer.
Been running strong for a few years now.
The foam backers already have holes in the bottom of them to slide right on wood dowels. I chose wood instead of PVC because if I accidentally hit one, I don't want shattered PVC all over my yard. The wood on the other hand will just naturally decompose on it's own.
I cannot recommend this highly enough. The price is great, and the function is excellent.
You can likewise raise and lower the height of your targets based on how long or short you cut the wood dowels too.
It's totally worth the very small investment.