Cage Cat paw-proofing grids and lid - what to use?

I know I've brought this up at some point, but I can't for the life of me recall what it was recommended that be used to safely attach to the cage to prevent cats from sticking their paws through the grid holes and, yes, even the closet shelving lids. (I feel like it's assumed cats' legs won't fit through those, but alas, all three of my cats' legs sure do! Even the tubby cat's lol)
As I'm planning a pretty big cage revamp, I wanted to see if I can go ahead and pick up the material to cat-proof the cage so that we no longer need to keep a sheet over the cage.