We have a fab bullmastiff, 20 months, male. He is perfect in 99% of his ways. Obidient, loving, good with people and other dogs he knows, however: it has happened occasionally that he will attack and pin down other dogs whilst out on his walk. They do not provoke this attack.
We have just bought a halti to see if this helps and are willing to try anything as he is a large dog & needs to be atopped! We had him neutered about 4 months ago but this did not change his charaster at all.
We would appreciate any advice anyone can give us.
Thanks

hi take him along to the vets first, for a ckeckup,to make sure there is nothing wrong with him that is changing his behaviour, and ask advise from your vet, he should be able to recommend a good behaviorist, the sooner you  get help the better, i ha d this with one of my dogs, its takes alot of hard work with a good trainer ,but hopefully things will get better.

good luck