I am looking for some advice for my friend who has a young boxer bitch (10 months) who was spayed a few weeks ago.  She is a typical boisterous boxer who 'boxes' any dog that goes near her but has generally been quite friendly with other dogs.  She has recently taken a dislike to most other dogs especially if they are small and even started a fight in pets at home last week.  She is scared of larger dogs but bullys smaller ones.  it only appears to be my friend and her partner who have problems with the dog being aggressive as the dog walker says she is ok.
I've suggested either keeping the dog on a lead all the time or a muzzle.  Her recall isn't great so calling her back when there is another dog on the horizon isn't going to work 100% of the time.  She is toy rather than food orientated but even a favourite ball wont bring her back when something more exciting is on the horizon.
Daisy has been babied by the family and sleeps in the bed and has run of house and my friend wants to know if taking away all priveledges will help with the aggression as she is very jealous and doesn't like any other dog going near her owners. 
She is willing to try anything but isn't keen on using a muzzle and doesn't think it is fair to keep a dog with the stamina of a boxer on lead exercise.
Any advice welcome as this is taking away the pleasure of owning a dog for her.

At the risk of sounding critical, and without being in full knowledge of the facts, it sounds like the boxer should have been socialised more thoroughly or just better - with other dogs.  7-11 months is the typical age for socialisation issues to rear their heads.  Unsuspecting owners with puppies assume that everything is going to be fine because their little puppies aren't showing any aggression or temperament problems - however, it is just latent through this period - then their puppies reach adolescence and suddenly all these socialisation issues rear their heads.  Even though I thoroughly socialise mine, I never heave a sigh of relief or let up on the socialisation until the first year is over.

Your friend now has the choice of either managing this behaviour or solving it.  To solve it, she will need to see her vet for a check up (which would be a good idea anyway, just to rule things out) and then ask the vet for a referral to an APBC behaviourist: http://www.apbc.org.uk/members.php

Not letting another dog near her owners is called resource guarding.  The resource that she is guarding being her owners.  Again, this is a separate issue and will need working on with a behaviourist.

There are no quick fixes - it will be a long process to help her.

To manage this behaviour, and until it can be solved with a behaviourist, you are right - she will have to be muzzled and on a long line, at all times.  She will get adequate exercise on a long line.  If your friend doesn't like it, tough - her owners have failed to train an adequate recall and they have an aggressive dog, and these two things mean she needs to be on a long line and muzzled.  Either one of these things would mean the same - both together just mean it doubly so! 

could it be related to getting spayed as the behaviour has got worse since then?  She is a lovely dog with people and great with children but just doesn't like other dogs.  Is there any way they can give her extra socialisation now without making her worse since she is still a young dog and therefore should be fairly open to change.

Well, there are some theories about spaying and aggression being related, although they are far from proven and although the dog would have had to have a predisposition to aggression, to begin with.  But that doesn't help anyway - you can't de-spay her.

As for extra socialisation to compensate now - well, you see, it's very tricky when the thing which the dog is badly socialised to is other dogs.  Because you can't control another dog to the extent that you can control a food bowl in resource guarding aggression, or even a person in people-related aggression. 

You also have to consider the welfare of the other dogs you are working with, should things turn nasty - in inexperienced hands, rather than curing your boxer of aggression, you will end up making the other dog you are working with aggressive as well!!!  Like I always say - aggression is contagious.

Working on your own, the best you can hope to do is to keep the boxer muzzled and on a long line at all times.  When she is on a shorter lead, you can practise the "watch" command and develop attention so that eventually the owner can walk near to another on lead dog without her showing aggression (because she is focused on her handler). 

But if you're talking about - socialising her to be happy interacting with other dogs, greeting them, even playing with them, then you really need an expert behaviourist and should follow the advice in my first link above.  Again - if you attempt that type of thing on your own, you will potentially end up just making the other dog aggressive also and it's a recipe for disaster.

thanks,
I'll pass the messages on to my friend and she can take forward the suggestions and try to get some one-to-one sessions with a behaviourist.