Foster dog arrives tomorrow!

We have a foster dog joining us tomorrow, and I'm a bit apprehensive about how its going to go down with our three boys.
The story in a nutshell is:
Friend of a friend (isn't it always!) had a girlfriend who had a bitch, he had a dog, accidents happened bitch got pregnant, complications in pregnancy, vet had to perform emergency surgery all pups died, bitch almost died but recovered, girlfriend now hates boyfriend and boyfriends dog, boyfriend leaving country to work for six months and can't trust girlfriend not to be mean to his dog so temporary home needed urgently.
So tomorrow we pick up a three year old black lab, we have three dogs one castrated two intact, the castrated dog is boss of the three and although not aggressive towards other dogs hates having his space invaded, he will pull a mega huff for the next couple of weeks so will need lots of attention. Our youngest will be fine, he'll enjoy having a dog his own age to play with so I don't anticipate any problems there, our eldest should be okay so long as the new dog submits to him, we've been told that the dog we're picking up is well socialised so fingers crossed we'll not have too many problems but I think it'll be a semi traumatic couple of weeks while we undergo the transitional phase.
The other concern I have is what happens after the six months, the owner has already left the area, we've never met him and don't know anything about him, in my mind I think he'll probably not come back for the dog as he's been pretty half assed about everything leaving it with other people to deal with, he left it with a guy who he knows is planning on going abroad for a couple of months himself. After six months I'm probably not going to want to give the dog back, and he'll be pretty well established with our dogs by then and they pine for each other when seperated, I imagine its going to be a difficult situation!

Has anyone got any experience of doggy fostering and if so could you relay your stories (good & bad), what happened, did the owner return and did you get over losing the dog or did you end up with a life time doggy addition to the family?

Foster carers usually have the back-up of a rescue organization so that, if things go wrong, the dog has a place to go to at short notice. I would try to ensure that somewhere else is available to take this dog should you find that your own dog/s will not accept him or that he will not accept them. Have you met the dog and assessed his temperament?

I would imagine that you would need to speak to the actual owner as you would surely need his permission/approval for any veterinary work that may be necessary should the dog be injured? What about costs of any veterinary treatment? Is the dog insured? Also you need confirmation that the dog is vaccinated and has no on-going health problems and that the owner does intend to take him back after 6 months.

If the owner decides not to take him back then you need contact details in order to have the dog signed over to you should you wish to keep him. You don't want the owner turning up some 18 months later and demanding his dog back, which he would have every legal right to do.

Sounds like it could be messy, but I hope it all works out for you, your dogs, and the foster boy

fingers crossed it all works out