hmmmmmm * looks at her nibbled sofa*
umm first id make sure they cant get under or round the back of it, mine are not too bad just a few nibbles
Personally if you wish to keep it new and chew free id just keep them out of the room the sofa is in, the new smell will move likely attract them into a chinning frenzy,
you could try washable huge throws, NIC grids perminatly round the back and sides