I had a Lindam playpen that doubled up as a barrier, which was fine for the first 30 minutes I put my LO in it. He hated being in it as it was too confined, and as he could already stand up at 7 months, he just used to rattle the bars. By 8 months he could drag the whole thing across the floor whilst in it, and by 9 months, he could topple the whole thing over on his side while he was in it.
We have wooden floors so although the playpen/barrier, is heavy, it was easy to slide around to move it. It may be different with carpet though as it would provide more grip, but it ruined our flooring.
To be honest, I think regardless of the things you use, kids will always find away around it, by pulling it off etc. Personally, I don't think you can go crazy and protect a child too much from it's own environment, as it's their own environment! Perhaps a playpen and/or stairgate is all you need?