Dear 100 Hour Board,
I like deviantart.com, because I like looking at all kinds of art by artists of all different levels. I think that some of the art is really inappropriate though. Is there a similar website with cleaner art?
Unfortunately, Deviantart is probably the most popular and has all types of art. And honestly, I think you're going to find similarly mature content no matter where you look. If you're looking mainly at graphic design, dribble is well known and great and graphic design is normally clean. For photography, you cannot beat 1x. It is curated, so it's a smaller collection of professional work and has only photography but is truly spectacular. 1x is good at marking nude content so I don't think you'd have to worry there. Typ.io is a little bit different but you still might be interested; it shows off typography examples (mainly from websites) of font choices. Pretty interesting, clean, but probably not what you're looking for.
I did a search for "Deviantart alternatives" and a few sites came up but they seemed (1) smaller and less popular then Deviantart and (2) just as risque, even just looking at the front page. You can do the search and check out some of the results to see for yourself if they are any better, but I don't think there is a solid replacement for Deviantart as a whole.
As you may already know, there is an option to hide mature content on Deviantart. The content is hidden by default, though, so it's probably not what you're looking for.
In my admittedly limited time on the site, I have found some pictures of people who couldn't get away with being on BYU campus, but I couldn't find anyone wearing anything that would get you arrested if you wore it in, say, downtown Salt Lake. If your filter's on and you've run into explicit material, then I'm not sure what you're doing differently from me. On the other hand, if you're hoping to find someplace on the internet that has a wide variety of user-generated content and maintains an LDS level of modesty, don't get your hopes up. Deviantart is successful because it is open to everyone, and being open to everyone means that no matter who you are and what your standards are, someone is going to post something that you do not approve of. Like Ozymandias says, you're probably going to find the same sort of thing no matter where you go.
Sorry we can't be more help, and best of luck!