When Monty first joined us he used the sofa as a litter tray a lot (think several times a day). The easiest option I found was just to dig out an old single duvet we had lying around, buy a couple of cheap duvet covers (our local Wilkinsons had a set for £5.50) and throw that over the sofa (fabric sofa, if it helps). Then I just had to change the duvet covers over every few days, wash them, and back on again - and in the meantime, we could bundle the duvet up and onto the floor whenever we wanted to use a clean, dry sofa. I think we got slightly lucky in that our sofa is one of those with a fringe of fabric that hides the legs and gap to the floor, but Monty has never shown any inclination to chew at it - unlike everything else in the room - but the duvet worked just fine until he calmed down and started using his litter tray, and no other problems so far. He will dig at it occasionally, but he's never managed to do any damage that way - although if I was worried, I could just put the duvet over it againI'm not going to be heartbroken if he ruins the duvet cover.
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