Well: this is almost certainly manageable, but I'd definitely stop doing the two things you have mentioned. First: please never roll a dog on its back!!
This is a quick way to end up with an aggressive dog and also is a totally unecessary and overly physical way of managing any dog (and can create a dangerous dog, too!) but especially a breed as gentle as cavaliers. This is more than likely making things worse, and may very well have pushed Leo into this more aggressive state of staring down Milo etc, as you are linking the unwanted behaviour to an aggressive response that will just keep linking fear to the the aggression causing more aggression. The alpha roll
has been solidly discredited by many canine experts -- wolves and dogs do not actually roll each other on their backs as a natural behaviour except in the most extreme and dangerous situations -- this is not the message you want to give your dog when he is being aggressive with a puppy!
A half hour in a bathroom is also really long. A time out only needs to be 5 or 10 minutes. Use the occasional time out like this -- making no comment or scolding, though you can use a negative marker phrase like 'too bad' (not 'no' which is overused by everyone and means nothing), just gently lead Leo into his time out space and then after 5 minutes, let him out again without comment.
Consider this in human terms -- if you had a 5 year old starting to hit a 3 year old sibling, what is the easiest, most constructive thing to do? Separate them!
Watch and learn what sets off their fighting. Reward the older child for desired behaviours and playing nicely.
How productive would holding the older child down be? Or slapping them? Or shouting? Not very. It is the same psychology with dogs: management and motivating desired behaviours, not punishing unwanted ones (which doesn't give the dog any behaviour to do as an alternative) is the way you want to go.
I'd advise finding an APDT or CCPDT accredited trainer to vcome in and give advice on how to deal with this behaviour as a management issue and to address the aggression with a rewards-based programme to get the desired behaviour rather than creating more fear. You can find accredited trainers in your area via
www.apdt.com or
www.ccpdt.org
But the basic answer is: this is behaviour that started as some common jealousy but now has intensified to a dangerous point, and this is going to escalate into something serious unless you start to manage the situation. Keep them apart in touchy situations and *prevent* then being able to do the things you don't want.
For example, food is a typical flashpoint and how can a puppy defend its food bowl against an adult dog? It won't now -- but give him a couple of more months and they may rip each other apart if Leo tries this. They need to be fed separately in crates -- never, ever, ever where they can feed from each other's dishes. Give them 10 minutes in a crate to eat and then food goes away til the next meal; never leave food down. You will probably find there are other trigger situations that bring on stares and potential fights -- for example toys or chews. These also MUST be given separately, a good distance from each other and you need to supervise the whole time. Attention to the dogs may also need to be separate but equal -- don't pet one when the other is right there; either two people give each dog separate attention or only give attention when the other isn't there. They also need equal, separate time from you. Have you done any obedience with Leo? If he has good self control from a solid base of training he will be less likely to do this sort of thing and you can manage him more easily -- be giving a look command and getting him to focus on you immediately when you catch him getting aggressive.
The staring is very dangerous -- that is the last step before a serious fight.
You can try these basics and see how they do, but if you are uncertain, I really think you need professional advice at this point as you do not want Milo to end up seriously hurt or worse, and it would be very helpful to have a professional trainer come in and observe how the dogs are around each other and give management and training advice (rewards, not punishment based
). Some dogs just do not care to have another around, or not the same sex, or not one particular dog and will get along fine with another. A female also would have been a better choice I think -- while cavaliers often have no problems in two of the same sex, generally you will almost always get a better chance of a good friendship with the opposite sex as there are none of the typical hierarchy issues between them. But most issues like this can be solved with some smart management and what you need is just to get some good advice from a trainer. Until then, do not let them into situations that can cause flare-ups.
I'd also recommend trying
this book.