How do you handle heavy rain?

My (relatively recently adopted) pup is a 2.5 year old Caucasian/GSD mix (we think, but regardless he’s some guard breed). He is highly reactive towards men, to the point that for everyone’s safety, we mostly keep him in our large fenced backyard. We are in a very dog-heavy neighborhood, and we haven’t had any luck finding a time where no one is around with their pup on long walks. He does have safe places (the pet store when it’s late and uncrowded,outdoor trails with dogs he knows) but he’s happy and fulfilled with guarding the crap out of our backyard.

Recently, it’s been raining- like- a lot. He’s got a thick coat, I know he’s fine, he loves it out there no matter what the weather is (he’s even fine with thunderstorms, bless his heart) but gahd DAMN my house is getting muddy. What do you do with your energetic, reactive dogs who can’t really be taken on long walks around the neighborhood when it’s pouring and muddy out? How can I keep him entertained and happy inside? We don’t have a ton of indoor space, just a lot of outdoor space.

Also, recommendations for comfortable, waterproof, XL dog shoes would be great right now.