I'm not convinced that dog boots are ever necessary. Wild dogs can't afford shoes. Sled dogs run all day barefoot in sub-zero temperatures. I have four random little mutts between ten and twenty pounds, and even they rarely have trouble in the winter. I took one of them out for a run today at 15 deg. F, no problem.
Salt is a problem. If there's a lot of salt out, I'll rub a sealant into their pads before we go out. Lots of things will work -- lip balm or lanolin are my favorites, but petroleum jelly would probably do in a pinch. But whatever you use, the most important thing is to simply wash the salt out of their pads after they come back in. I've done this for almost a decade in Colorado and none of my dogs has ever had a cracked or frost-bitten pad.
Salt is a problem. If there's a lot of salt out, I'll rub a sealant into their pads before we go out. Lots of things will work -- lip balm or lanolin are my favorites, but petroleum jelly would probably do in a pinch. But whatever you use, the most important thing is to simply wash the salt out of their pads after they come back in. I've done this for almost a decade in Colorado and none of my dogs has ever had a cracked or frost-bitten pad.