Roommates Dog

What's up GC
 
I'll try to spare some of the details, but long story short, my roommates dog is driving me nuts. She's a lab, great dane, pit mix, and sweet as hell. The only problem: she isn't potty trained.
 
So I live in a two bedroom with my roommate and his girlfriend.  They brought the dog home in late May of this year, and after 5 months, she is still pissing and shitting all over my belongings. One day, I got home and she had shit on my bed. Yes, on my fucking bed. Yesterday I got home from a long day of work and class, sat down on the couch, and sat straight in piss. Needless to say, without my toke, I would've flipped the fuck out.
 
Technically, it's my roommates' girlfriend's dog, but I feel like I'm the only one that has to clean up after it. Even when we first got her and tried crating, she shit and piss in the crate, and I was the only one there to clean up (3 times before we abandoned the idea).  So the point is, I feel like I'm getting the raw end of the deal.
 
Attempted solutions:
1. We tried keeping her outside, but she gets under the house and plays with the neighbors dog who is "neglected" and has some skin disease.  We tried fencing the area where she gets under the house, but the dogs just dig underneath, or break the fence wherever we try to stop them. So, they don't want to leave her outside because she won't recover from the disease she already has gotten.
 
2. They tried leaving her inside while everyone is gone. Doesn't matter where they try and lock her up, I end up having to clean up her shit, piss, and mess created by her chewing. I want to ask them to leave her in their room instead of out in the living room, but they don't want her to mess all over their stuff. It's kind of fucked, but if it's their dog, they should be the one's taking care of it, not me.
 
I honestly don't know what to do. I've already told my roommate that I'm tired of cleaning up after her, and that was two weeks ago. Still, I'm coming home to piss on my bedroom rug, or piss on my grandma's antique couch. Does anyone have any advice on how to deal with this situation?
 
Maybe I just needed to vent (again), but it's been like this for a while. I understood when she was still 3-4 months old, and was getting settled in. But now, it's 5 months later, and nothing has changed.  My roommates girlfriend (who's technically the dog's owner) has done nothing about it. I mean I have literally never seen her clean up a single mess. So again, any advice is greatly appreciated.
 

 

 
It's technically my roommates house, but I've been here just as long as him. Appreciate the advice. I probably need to be more direct, because if she does something, I'll just clean it up because I don't want it sitting there.
 

 
Haha nah it's not Luke. The problem with the reward process is that they work in the service industry, so they are gone most days/nights and aren't home enough to make it a routine.