Here's a list of Vieta members - it looks like three of them are in KT Bern, although I'm not sure if close enough to you. I'm afraid I don't have any personal experience of these folks, but I found the list while searching for an APDT-like umbrella organization of trainers here. Seems worth investigating.
http://www.vieta.ch/beraterliste.htm
I'm a big fan of clicker training, having seen it work in so many situations. Clicker training is a positive way to use classical conditioning to motivate your dog and shape behaviors - have you looked into that approach? For instance,
http://www.clicker.ch/semi.html
Although this group is in Biberist, they hold a seminar in Aarwagen Be - is that anywhere near you?
(Their site has a good write-up of clicker basics in English
Also, try the SKG:
http://www.hundeweb.org.
Click on 'Erziehungskurse' for a list of SKG member schools in KT Bern.
I have found that trainers and behaviorists here vary widely in outlook and practice. I have met some very good trainers here, and some absolute numpties whom I would not let within 10 km of my mutts. You should have a long, detailed talk with anyone you are considering working with - make sure he/she has solid experience with dogs similar to yours, knows the technical and practical side of training, and - most importantly - follows ideas and methods you agree with. And - although this should be a given, it sometimes sadly isn't - make sure the person you work with actually likes dogs and appreciates them as pets and not just as breed stock or something to win rosettes with.
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One of the most respected behaviorists specializing in aggression issues is Angela Stockdale - she is based in the UK so a visit may not be possible for you, but her website is full of good ideas. You could write to her for advise:
http://www.dogpartnership.co.uk/
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And while you are searching, can I recommend some very good books which might help you and your dog?
Jean Donaldson - 'The Culture Clash'
Pat Miller - 'The Power of Positive Dog Training'
Karen Pryor - 'Clicker Training for Dogs' and 'Don't Shoot the Dog'
Brenda Aloff - 'Canine Body Language, a Photographic Guide' and 'Aggression in Dogs - Practical Management, Prevention and Behaviour Modification'
Turid Rugaas -'Calming Signals'
All well respected trainers and behaviorists.
I would also recommend trying TTouch with your dog - this isn't a training method, but rather a way of calming your dog and communicating with him, which greatly adds, IMO, to training success. I found this to be a valuable tool when working with my traumatized collie - TTouch helped break through his barriers so that he could be receptive to training and desensitization, and I continued to use it as a safety signal when we encountered a high stress situation. For info on TTouch:
http://www.lindatellington-jones.com/whyTTouch.shtml
(The website and philosophy is a bit too 'new-agey' for my taste, which led me to be very skeptical at first - but to my surprise the technique did indeed work for us. )
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I am a strong proponent of positive reward based training, especially when helping a dog to overcome fear-based behaviors (aggression and socialization issues are often a response to fear). I firmly believe that punishiment/dominance theory/militaristic training can do serious damage to a dog, even more so when dealing with rehabilitation issues. I would be
very careful of any trainer who suggests this kind of approach for your dog.
If you are looking for private training then the fact that your dog isn't neutered should not be an issue. It could be a problem in some group courses, though.
I'm not in BE, so I don't know of a vet in your area, but I'll ask my vet (in ZH) if he can recommend someone and get back to you.
Good luck with your search, and with your dog. I'm sure you'll be able to work this out.