Agressive 7month old

[amstaff07]

I have a 7 month old American Staffy x English Mastiff who has been socialised and really good with other dogs until about a month ago. He is desexed as i was hoping it would avoid this a bit (my previous dog was agressive until he was neutered). I also have a staffy x Kelpie and they get along great. But lately he wants to eat every dog he meets, especially the big ones!!! He weighs almost 35kilos so is not small at all which worries me even more. He has agressively come into contact with 3 dogs in the past few weeks. I cant seem to take him anywhere off the leash anymore. I have no idea what brought on this agression but i think its that he is trying to protect me and our other dog. This is unacceptable does anyone have any ideas? I am going to muzzle him from know on, for his and other dogs safety but it wont fix the problem.
i have established that i am the alpha dog and he is great at home. please help.

[Blue]

Hi there- I love AmStaffs beautiful dogs - very powerful, but beautiful!
Please see:
social boxer turns aggressive
As you pointed out, you both have similar issues, and I will try to help both of you with them as they arise/progress. You will also probably be able to learn from each other's questions .
Blue

[mommyg]

I have an American Bulldog puppy, probably 7-8 months old. We adopted her 3 months ago. She is as sweet as can be. We also have two other dogs, one female, maybe Sheltie, and a cock-a-poo. The cock-a-poo is the only male and he is the oldest both in age and with the family. The problem lies in that the Bulldog has become very aggressive toward the cock-a-poo when he has a treat that she wants. She basically pounces on him and takes a hold of his ear and won't let go. The cock-a-poo is the most mild mannered animal but he will hold his own with her, to the point one of the getting hurt until we are able to break them apart. How do we fix this so that we can all live peacefully in the house. It is quite scary when they go at each other.