Dr. Corrigan, in his Rodent Control book, describes the use of stainless steel shoved into gaps as a very effective but only temporary protection. He does not elaborate on why it is temporary, but perhaps this is because of the eventual deterioration of the material or perhaps the rodents do have the ability to pull it out to reopen the hole. A very coarse steel wool might be more durable against the rat activity than a fine mesh, but copper and stainless steel are much coarser and might be jammed into the hole more tightly. Rats and mice also would have difficulties trying to pull the material out with their teeth. I don't know that it has as much to do with being painful on their feet as it does just a barrier that they cannot chew away. 

Regardless though, a more permanent and aesthetic exclusion would be, at some point in time, to replace the wool or mesh with caulking or concrete or wood or whatever material is appropriate for that point on the structure. This could then be painted over to blend in and with a little luck the gap will be gone and invisible.