I cover my car whenever it's practical - like it's gonna sit for a few hours. Been doing it for years. I use those cheap car covers from Pep Boys. They only cost like $30 and they last for a couple of years. They're easy to put on and take off, once you get the hang of it. The trick is rolling them up when you take 'em off. Kinda like packing a parachute.
Does it work? Here's a snap...
Covers tend to 'dust' your car, especially if it's windy, so I also carry a
'California Car Duster'...
Anyway, I carry a can of foaming spray window cleaner with me, and a shop towel. When my ride gets crapped on, I spray it, let it sit for a couple of minutes and CAREFULLY blot it off. Don't wipe it off, otherwise it'll scratch the finish. Sometimes it takes 2 or 3 tries.