[Sheenagirl]

I replied to your post because I am worried about the wellfare of your dog.
It sure sounds like your friend really doesn't care (or is naive) about your dog getting mauled and killed - he is probably thinking his dog would be the one that's okay or he wouldn't ask you to keep his dog.
You even go so far as to say you owe this friend - even if there is a "potential risk" for both you and your dog.
So, your mind is made up. Six months is a very, very long time to keep two dogs separate.
The Tosa would be quite capable of destroying a metal cage or enclosure. Also very capable of going through windows and doors - not to mention it isn't fair to keep the dogs locked up in a room for six months!
I hope you build an extremely heavy duty enclosure outside for the Tosa and do not let them together or even near each other for the entire six months.
You now know what lies ahead for you and your dog.
I truly hope everything goes well...