any recommendations? Been looking for weeks, they all seem to be too small, or designed for rectangular ottomans.

I have a square 35" x 35" cushioned ottoman which is my 65 lb lab mix's favorite spot to lay. It's 35-in square and 19-in tall, with roughly a 6-in tall cushion (non removable). We bought the Nolan Interior "Magic Sofa Cover" which we thought was doing a great job but then realized after several months, had let much saliva and other liquids seep through and stain the fabric of the ottoman. It's not waterproof at all. We need a similar alternative product that's truly waterproof. Something like a mattress liner but is square (35"x35") and perhaps decorative. Or, at least, just a liner we can stretch out under the Nolan cover. Prefer to not make it full height so the bottom remains exposed. Thanks! (xposted on r/dogs)