Geek straps do it for me.
Although, true to form, I went with the high-end ones for $3.00 each. I liked the reflective stuff.
FWIW, my old hybrid came with a plastic chain guard. While better than nothing, it certainly isn't a cure. Geek straps are the only thing that works 100% effectively, 100% of the time.
Unless you're an under-25 hipster. Then you can get away with rolling up your pantleg. Or wearing knickers.