I use Musher's secret on them. They've got boots, but both of them seem to slip in them no matter what because we don't have level ground. Dannyboy and Sharkly always wore them though, but we lived in town. MY limit outside in that is 30 minutes. I'm frozen by then whether they are or not.
Main precaution is to keep them away from streets that have salt or brine on them. THAT can tear their feet up faster than anything. If they get in any of it, wash their feet immediately when you get indoors again. There isn't really isn't any kind of de-icer that's paw safe. Even on the ones that say they're safe, if you start reading fine print, it says keep it off your skin. Why?
Also, keep the hair between their foot-pads cut as closely as possible. It can get frozen together and special care has to be taken to thaw it when coming indoors. Just keep a blow-dryer close for when you get in, and blow until their feet are dry again.