[McTaff]

If you get a car cover, make sure the inside is a soft fibre so it doesn't scratch, and the outside is waterproof.

The ones I have come with a dinky little pair of straps that go under the car and clip together to stop it blowing away, and have ends/corners that are elasticised. Never lost one to weather, and they've protected the car really well. Avid folks might even get a clip to anchor it to the wheel, but I've not had any trouble with them moving.

Works great, but getting the strap under the car requires laying down beside the car, not something you can do in a hurry. (If it's in a public place, then I don't know. I never leave my car in a public place.)

Best investment, though