forest after a rain — or the air is very humid —, and come back soaked, dry them well. if, on top of that, it is very, very cold, do wrap them up before going out.
dogs are very social animals. they like sleeping with the rest of the family. if they prefer the garden anyway, they must always have a place to take shelter in case temperatures drop suddenly, or something scares them.
if your pet sleeps normally in the garden, and is used to it, their coat has adjusted naturally. they do not get cold so easily. if they are not used to it, but want to sleep one night 