Like some I have a specific need to pet-proof my couch. I am a foster parent for cats in need of adoption. These cats tend to get conflicted on where they should do their business.
Sometimes they are trying to send a message like all cats, and sometimes they just aren't getting it. It's also well known that sick cats tend to go in abnormal places, pretty much anywhere but the litter box.
Going in abnormal places is not too much of a big deal, but it really depends on where that place is. Certain places like the bed and couch can be devastating when you later realize how difficult it will be to clean this mess.
For beds, most people know you can get the plastic sheets at wal-mart or target. But for couches, its a little different. You can enclose them in the plastic couch "protectors", but most people (like me) think those are overkill, ugly, and uncomfortable.
so after my last "incident" with my latest foster cat, i realized this is just going to happen again and again. The couch cushion liners are removable and very easy to clean. the cushions, however, are very difficult to clean, at least when trying to remove urine odors.
After throwing the liners in the washer and hang drying them, the cushions need to be neutralized with vinegar. soaking the affected area isn't easy and does not dry out like water. because it's foam (as are most cushions), it allows the vinegar to flow to the bottom of the cushion, where it stays there until you squeeze it out.
After that you have to rinse with water because vinegar doesn't exactly smell good. minimum cleaning time, 6 hours. if you dont have time to sit there and wait between steps, its prolly more like 16 hours.
so i thought about ways to waterproof my cushions so all i have to do next time is wash the liners. so i got a pack of 30 gallon (large) trash bags to use as cushion protectors. I removed the liners and enclosed my cushions in the bags, then replaced the liners.
in my first attempt, i sat down and realized I created a cushion balloon. the cushion needs to breathe a little so it can conform to my awesome backside. so i re-opened the liner and cut the edges, thus keeping the upper (and lower if the cushion is flipped) sides protected.
this allowed the cushion to breathe a tad more and sitting on the cushion was a tad easier. now it felt more like a hydraulic lift lowering me down as I could hear it releasing the air, but it's a small price to pay for the situation I am trying to avoid.
For people less paranoid than me, I suggest you poke additional holes throughout the bag, just not too big. air will be able to escape but will be far less likely to allow moisture into the cushion.
this works well enough for me, so I hope it works for someone else as well. however, this isn't a universal resolution. not every couch has the same size cushions so I can't guarantee you can enclose them as I did.
If they don't fit, I suggest you cut the bag down the middle and just wrap as much of the top side as you can. you don't even have to use trash bags, you can also use painter's plastic wrap. i only recommend trash bags because they tend to be very stretchy.