Any ideas for solving this problem
I have my dog with my on a visit to my sister's house. She has a male, unfixed dog which won't stop humping my dog, who though bigger is old and has problems defending himself so she is literally being humped into the floor. Her dog has gotten aggressive with both she and I when he has been corrected for this behavior and goes right back to the behavior no matter how long a time out has been. Any suggestions.
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Keep it mellow. 
Not that you can probably tell her that, but really... very irresponsible pet ownership there. 
That's wear some of the aggression is coming from. But the larger problem is that the dog has no problem being aggressive with other people including its owner. That HAS to stop. The dog humping your dog all the time is a lot more about dominance than mating. If your dog is not in heat this male should have really no interest in constantly trying to mate with yours. The dog has both a dominance and aggression issue that MUST be dealt with before he hurts someone. Frankly, I think a specialist is in order in this case. A dog that is aggressive with its owner is a really serious problem.
You can also do some reading here to get some ideas on where to start with your sister establishing who the boss is since this dog clearly believes that HE is. When that happens they'll act like any other pack leader dog and discipline those people or animals that he disagrees with which may be barring teeth, snapping, biting or a full out attack. That's the most important thing. There is also info about dominant or aggressive dogs here, but the relationship between the dog and your sister has to change first... that's the single biggest problem.
http://leerburg.com/structure.htm
I'd start with the article called Establishing Pack Structure. Under the "Training Articles" heading there's also a ton of articles, free videos, ebooks, etc. of specific issues like dominance and aggression. The free videos are great, too.
Keep in mind that this is your sister's dog, and it has to be her that needs to work on her dog's behavioral issues. Honestly, I wouldn't want to be around this dog whether I had my dog with me or not. Since this dog is already behaving aggressively toward its owner, I really think that hiring a professional ASAP is probably what's needed right now. Keep in mind though that the good ones aren't so easy to find, and a charlatan will only invite bigger problems. Your sister should ask her vet for a recommendation for a professional trainer that's has a lot of experience with dogs that have dominance and aggression issues. But not all vets really know who is good and who isn't themselves.
Your sister can also try calling whoever is the head of your state's dog department... whatever their title this is the person that will know more than anyone else who the good trainers are and who are a waste of time and can give you a list of professional trainers and can make a good recommendation of who to use. For some reason this department is under the umbrella of my state's agricultural department, and apparently most state's also have it set up that way. Whoever they are they'll be located in your state's capital (well, your sister's state in case you two live in different ones). I found out who my state's person was by calling my township's administration office, and the receptionist already knew who the person was, where their office was, their phone number and even forwarded my call directly to them. I don't doubt that your sister's township administration offices will know all that stuff about who's who in your sister's state and how to get in touch with them. Unfortunately, in my state dog trainers don't require any education or certification so anyone can call themselves a professional dog trainer... which is undoubtedly why we have so many charlatans. After having a long interesting conversation with the guy in my state several years ago I learned that most states don't have any special requirements for professional dog trainers.
In the meantime, I strongly suggest that this dog is kept away from anyone that doesn't live in the house, and definitely don't let him near your dog. I also strongly recommend that you don't get involved in disciplining this dog yourself since it has gotten aggressive with you already. Whenever you visit he needs to be kept in a crate or on a leash even in the house or in another room or something.
Best of luck to you and your sister. With the right approach this dog's behavior can be changed.
