I personally prefer sissal, that way Pookie didn't get the idea that regular carpet was ok. But some cats may prefer other textures, and you may need to try a variety before finding one (or more) that the cats like. I have several scratching posts throughout the house, in areas that he and his sister tended to scratch, and some are upright, others are on their side. He uses all of them. I got the sissal from the hardware store and wrapped the ones that were covered in carpet, then rubbed the catnip on it to really get the attention.
When they were young, if I caught them scratching something I didn't want scratched, I would make a harsh sound that they understood meant "Mommy doesn't like this," pick them up, take them to a post and very lightly drag their feet over the post, all the while saying in a happy voice "Good boy (or girl), that's a good boy (etc.)." They very quickly got the idea and would start scratching the post, and I would keep praising them. Literally every time they used a post, I would praise. Positive reinforcement is very important. To this day, every time Pookie uses a post, I praise him. Rarely does he scratch something he's not supposed to, and if he does, I make the "sound" and he runs and goes to a post instead (where he gets the praise). Once in a while, I do rub catnip on the posts.
I never needed to cover anything to deter them from scratching. Usually I just made the noise. But I think it helped to have at least 1 post in every room, near the areas they wanted to scratch (like the back of the recliner), and in different positions.
If I think of more, I'll add it later. I hope this helps!