I would recommend a neoprene type cover that goes over the whole scope, or indeed a neoprene or lodencloth type cover that goes over the whole rifle. When its wet and mucky they keep everything dry and also protect against the bumps and scratches, yet are very quick to remove when a shot presents itself. I have always found that flip up covers just break, or get in the way of hat / cap / bolt handle etc. I have need of a cover to keep rain and shite out of my optics, I also want to protect the rifle itself.