I have a three light switch panel in my living room. One of the light switches turns everything in the living room off..instead of rewiting I would like to buy a cover to place over the one switch to prevent anyone from turning it on or off. I don't know what they are called or where to get them. I do know they exist though because I have seen them. They are a small piece of domed plastic that screwes over the light switch. can you help?

Thank you!