No, it doesn't seem appropriate. Fanfiction is a form of creative writing that often involves exploring characters in new ways, but this description crosses the line into something that is more likely to be offensive or inappropriate. It goes against the general spirit of positive and respectful fan - created content. Fandoms are meant to be inclusive and family - friendly spaces in many cases, and this kind of theme doesn't fit well into that.
One possible story could be that the wife was helping with the planting on the farm. Maybe she was kneeling in the muddy soil to carefully place seeds, and in the process, she got covered in mud. It could also be that she was trying to rescue a lost animal in a muddy part of the farm.
No, it is completely inappropriate. Public nudity is not acceptable in most societies and goes against moral and social norms. Even in the context of fictional 'free stories', it promotes behavior that is not in line with proper values.
I'm not sure where you can specifically find a 'naked crawl leash Draco' fanfiction. Fanfiction websites like Archive of Our Own (AO3) or Fanfiction.net might be good places to start, but you'll have to search using relevant tags and keywords carefully. Some works might be restricted due to their rather unusual or potentially inappropriate themes.
Rather than focusing on potentially controversial themes like 'naked crawl collar', it would be better to look for Draco - centric fanfiction that focuses on positive character development, his relationships in a more appropriate context, such as his friendships or his journey to redemption. There are many great Draco fanfictions out there that explore his complex character in a tasteful way.
One plot idea could be Draco having to do a naked crawl as a part of a dare in a magical forest. Maybe he's trying to prove his bravery to his Slytherin friends. Another could be in an alternate universe where it's a rite of passage in a wizarding cult that Draco is unknowingly a part of. A third idea is that it's a curse placed on him by a rival, and during the crawl, he discovers secrets about the magical world around him.
Perhaps the wife was out on a hike. There was a stream crossing that looked easy, but as she stepped on a mossy rock, she lost her balance and landed in the muddy bank of the stream. She then had to walk back home with mud all over her, making quite a sight and having an adventure to tell.
There might be a story where she was playing a game with the kids on the farm. They were having a mud - based treasure hunt and she got really into it, getting covered in mud in the process. Or she could have been watering the plants and the hose burst, spraying mud everywhere and covering her.
In the context of the story, it could lead to social ostracism for the character. The community in the story might shun her and her family. Also, it could send a wrong message to readers, especially younger ones, about acceptable behavior. It might make them think that such extreme and improper behavior is okay in certain situations, which is not the case.