I have this rain coat from dog.com
Trendsetter Jacket with Plaid Lining - Dog.com
I have one for my morkie girl and also my weimaraner (75 lbs). Here in Georgia it doesn't get to cold, even when it rains but if it does I put a hoddie on underneath and the rain coat over the hoodie. I also saw on dog.com they has some larger coats that might cover more of his body for a walk, we only use them to go out to potty
I've also seen some cute leashes that have an umbrella towards the end of it covering the dog, not sure how practical it would be though
