Hi Doug, and welcome to the Forum.
Your problem is a common one, chickens are no respecters of lovely grass lawns. Do you also have a run with their coop in it, which you can shut them in when the weather is bad, or indeed use to ration their access to the whole garden? A run with strong mesh sides and top will also protect them from predators, especially foxes, which at nowadays very common in gardens and can strike at any time of day or night. It sounds as if you have made them some shelter, but they haven't had the sense to use it. If you can make them a walk-in run of at least 6square metres of floor space (ie, 2 sq. metres each, more if possible or if you think you might like more chickens in time) then it will be fine to keep them in there over the winter, otherwise the garden will become a quagmire once the grass stops growing and the winter rains really begin. You can fill the base of the run with a choice of bedding materials, so they can have drier feet and enjoy scratching around in it. Many people use wood chippings, sometimes available cheap or even free from tree surgeons. If you can give the run a roof, at least over part of it, and also cover the sides of at least one end with either clear plastic tarpaulin or removable panels of corrugated plastic roofing material, the wind and rain won't blow in sideways and everything inside will be much drier and more comfortable, for you as well as the chickens. Until you can do this, they will clean themselves up on dry days by preening and dustbathing (if you have provided a dustbath in a dry place, preferably under cover in their run) but until then, they'll just have to put up with some bad hair days. There are lots of threads on here about constructing runs, and many people with good experience of doing so.
As for the lawn, next year you could do as I do with mine, and pen them in a circle of chicken netting (the sort you buy for electric chicken fencing, see the Omlet site, but not electrified unless there are foxes around) during part of the day, to eat the grass. I move the netting on every few days, and treat the grass as a food crop, keeping it mowed, picking up chicken poo, and watering it in dry spells. It does need to be in good condition before the hens get on to it, though, as they will instantly excavate any bare areas, as you have found. Mine isn't too bad, even though it has had 4 hens and a cageful of quails on it all summer, though I shall rest it once it stops growing for the winter. This system also keeps the chickens off the flower beds, if this is important to you. If you now have bare areas on your lawn, you could consider re-seeding them now, or patching bigger areas with turf, leaving them to grow in over the winter, and keeping the hens off until next Spring. Yes, it's lovely for them to be able to range freely, but we back garden keepers have to share the garden with them, and if they destroy it, it's no good either to us or to them!
