What do I do if it is raining and my little one needs to go out? You can either train them to use a pee pad, and a variety of other methods or you can put a raincoat on them. But, it must cover their underside or it is a waste of your time. Why? The mud will just cake on the underside and then you either have to let it dry or wash it.
Throw in a Havanese that doesn't like the rain - yes there are some that hate their feet and underside getting soaked and solutions are needed.
When selecting an outfit make sure it goes on fast. You are not going to stick to anything that takes too much time and effort. I know - I have a basket full of possibilities that do not work. Make sure it is waterproof and covers the underside. You can always deal with the feet easily but try washing a tummy without the rest. It's a tad more difficult.
But most of all - always BRUSH your dog after getting him or her wet and you will avoid many mats and knots. A wet dog - especially through that blowing coat stage, can get felted hair, something you really do not want.
When Kat jumps in the pool, we give him - well, I give him a brush over to keep him from tangling. He has a show coat but those that don't want that bother but love their dog to swim - cut them in a really cute puppy cut. You will be glad you did. Us - we just like the long coat and so we brush after swimming.
Just a tip as I am watching the rain.
PS: for a quick outside and do your duty...no I don't brush the crew. It's only when they get sopping wet.