Yes, cats chewing cords can be deadly.

Split wire loom tubing/conduit is what you're looking for to protect them. You can buy "pet" targeted products with a big price hike but they're the same thing. The 1/4" should fit normal electrical cords and phone cables. The 1/2" inch is for larger/thicker cords like those on surge protectors, space heaters, and air conditioners.

I have a cat that chews everything including walls so all of my home's cords have these covers. It's important to rule out dental issues so ensure your vet does a thorough checkup. Otherwise, it's behavioral. I find my cat chews less when I play with her more and give her lots of entertainment like laser toys. You might try that.

Re where they've urinated: I suggest you thoroughly clean that area with an enzyme solution (as cats want to keep peeing where they've previously peed) and block their access to the area.

Good luck.