[bliss7373]

If you explain the danger to your friend, perhaps he would look for other options? I hate to think of you putting these dogs (and yourself) in such a stressful situation if there are other solutions.

Also - in my honest opinion, I think they should be separated even while you are home. From your post, these dogs have tolerated each other in the past but are not friends. There is no reason to have them loose together. Especially if it is just you trying to monitor and separate them if necessary - as you said yourself, if they get in a fight, it is unlikely that you can separate them successfully. It's just not worth the risk.