Pedro, I want to tell you, I think your telling us you are doing something you have heard from TV. Please, TV is fine for a lot of things, but training dogs, dealing with behavior issues, isn't the place to get your only info.
Dogs deal with aggression from humans with aggression. If you notice, the best behaved dogs are calm and know the human will be calm and consistant. Overdoing punishments only makes the dog feel that your not in control.
There are many ways to help a dog turn around any behaviors that are not acceptable.
Anything harsh, will NOT work..please, trust me, it won't.
You need to help your dog learn to talk to you, and you need to learn to talk to your dog.
This only comes about with calm, consistant behaviors from the human.
Honestly, we are so happy you found us and we are really trying to help you bond with your dog..it doesn't take a hard hand, it takes a soft hand with consistant rules.