Ok So I have a 2yr old male  Catahoula Charlie whom I have had since he was 8 weeks and he is a wonderful dog. Well last month I volunteered as a foster and picked my foster pup up last Thursday. Everything was fine, she was very shy and just sort of checking things out. Well by about Saturday she had really taken to me and would follow me around and even come when I call her. Almost one week to the day I have problems! My foster is an Australlian Shepherd and she is just slighty bigger than Charlie and she will just out of no where pounve on him and then all heck breaks loose. I yell NO and they stop,, but this last one was bad and Charlie has a pretty good cut under his eye and she has a small one under hers as well. Charlie is now pretty afraid of her and avoinds her at all cost, but she follows him around the house and I'm on pins and needles following them to make sure they don't fight. I have been rotating them inside and out to keep them seperated this morning, but I know this can't go on. Please help

To be honest, you shouldn't really move to dogs in together without checking out they will get on first. this is normally done over couple of meetings. also, neutral territory is always advised before you bring them home together. im guessing you are fostering for a rescue? did they mention this to you? if its as bad as you feel and you think your existing dog is under as much physical danger and stress as you state, and you dont feel you can cope with this situation, then i would return him to the rescue, assuming that you got him from one?

in the meantime, you will have to keep them separated. at the best, you need a home visiting trainer/behaviourist, as its quite hard to advise about aggression over the net when you cant see things for yourself.

Yes it is for a rescue and I did bring Charlie to meet her, but only once. I think that she is trying to take over his role as top dog. Thank you for your advice

actually, charlie's role might not be as top dog. top dog doesn't automatically assume its the first dog in the home, it assumes how the dogs see it. usually, in a dog-bitch situation, the bitch is the top dog. if you reinforce the wrong dog (not saying that you have), then you can make things worse. it sounds like you really need to speak to the rescue and/or a good trainer/behaviourist. 

I have been reading that. Thank you so much for you're help. They were getting along so well at first we were considering adopting her, but I don't want either of them to get hurt

Any dog takes a while to settle in and their true character takes even longer to come out sometimes months, so naturally she will have been quieter and getting used to her surroundings, a week on she is feeling much more confident, has got used to her new surroundings, knows that you are the one who feeds and walks her, you are her lifeline now and she will make sure that you know that and that any other dog in the house knows that too, she will fight to stay in favour as top dog for food, attention and anything else that is going from you.

Bitches as already said will most usually be in a more Alpha position than a dog, dogs generally except that bithces rule the roost. Catahoula Charlie will most probably take a more submissive role, not only is this new arrival a bitch but a much larger breed, his chances of having any say in the dog world are pretty low now.

There is every chance that they will live happily together, dogs and bitches don't generally fight once the bitch has claimed her new position things settle quickly.  If you intend to keep her, then up her pecking order quickly, there is no point in beating around the bush she will rule the roost anyway, so fuss her first, feed her first to acknowledge to your male too that she is now the Alpha. He will fall in line.

By all means allow her to show status by growling etc, in general that is all that is needed, your male is only putting up a fight due to her being new and this being his territory first, but he will need to back down and should naturally do that, if the bitch goes to bite your dog use a stern voice, then seperate her, let her know this is unacceptable, that it gives you displeasure, she will learn, at this early stage she will not wish to displease you, you need to show your authority over hers or she will be unmanageable once her feet are under the table, so segregate her and show disapproval and make a fuss of your male to show he is valued by you.

No bitch needs to attack a male to show authority, (bitch on bitch is another story) allow her to growl and snarl if needed to get the message across but no more than that is needed.

Just higher her status in the home and the two should live happily together, it's very early days and they are both adults so they have clashed, but everything will sort in the end.

If you need to leave them alone for now, seperate them into different rooms, until the bitch accepts you as the authority figure and your dog accepts her. :-)

Carrington thank you so much. She is truly a sweet dog as is Charlie and I would really like them to be able to live together. I will work with her obedience and keep you posted. Again thank you so much

if you feel to can handle it after all and that there is hope they will get on, then that is good news.
however, i would still advise you get help from the rescue or a trainer, as it isnt really safe to follow any advice re aggression without the adviser having met the dog/s and assessed the situation, routines, domestic circumstances, dynamics, relationships, body language, signals, and behavior of everyone in the home, incl the humans.
there could be all sorts of subtleties we arent (or you arent) privy to.

i'm not saying carrington's advice is wrong. actually i think it is a great post and well written. i had to move one female into a home with 2 other females, and did the 'allow growling' thing as well. even knew when to allow some small fights and when to intervene. however, i performed several meetings beforehand on neutral territory. everything worked out ok.
we can give you our educated experience, and it might even work, but it is still a bit of a risk.   

Thank you both. I currently Have Charlie in obedience and agility and I am going to have his trainer come to the house and see if she can hellp me assess the problem. Thank you again. Today has gone quit well. I have been monitoring them and when I can't I split them up. We have not had any fights since last night, but I have stopped a couple before they started. Fingers crossed

oh poor you to be on tender hooks all the time and for poor charlie whose home it is, i had two terriers one being a border terrier and the other was a jack russell, they lived together for nine years and had the occasional spat with each other, this left me on guard and i had to let them out separately. however somethng urgent came up and i had to ask my niece who lived with me to look after the dogs whilst i was away for the day, unfortunately they took advantage of my absence and the two had their final spat, tasha was killed and rosie had many cuts. it was terrifing for my niece and distressing for all of us. you should return this dog back to the rescue centre i think for fear of upsetting charlie and making him on guard to all other dogs, good luck and i think your marvellous to foster other dogs from a rescue centre, good luck in the future

Hi

I think you've done a great job in fostering and have found out some valuable information for the rescue but IMO it is time for the dog to go to another fosterer .  I foster as well and feel that the resident dog has to feel safe and happy with the foster dog and if not it isnt fair on the resident dog and if you dont want charlie to resent other foster dogs coming in the future then you should take his feelings into account now,

As I said this is just my opinion based on my own fostering experiences - I wish you luck with whatever you decide,

Agree MW184 :), i would take the dog back if my two resident dogs were on edge and didn't get on. Good luck and good on you for fostering :)