aggressive dogs extremely bad

Question
This is not a new problem.  All my life now (56 years old), each and every time I get a dog, he becomes ficious to the point where he is locked up.  Why?  I have no idea.  Example:  I recently got a collie mix puppy, fell in love, bought toys, played with him....my whole family adored this dog...Then he started snapping at people's legs (drawing blood), so I put in on a lead.  Then he started becoming more aggressive barking at other dogs, like my daughters smaller dog. So I pulled him on a chain to stop the fighting (can't go very far to start a fight).  However this one time, when he was barking at another small dog, I pulled him on the chain, closer to my legs to walk away.  He bit my leg twice (hard).  I did not fall from the hit, only because I was then afraid that if down, he would of continued the attack.  When I got him back into my room, he did his begging stance and was all happy.  Of course, I'm fumming (two serious bites & brusies from the knee to the ankle).  The thing is he had no idea what he did was doing was wrong, just started acting like a big baby again.....It got so bad, that I had to give him up to a junk yard man watching over trucks in a yard...He's now a killer.  Why?  That dog had tons of love as well as the others.....I want another dog, but I'm afraid they will turn out just like the others....its me, but why!  

Answer
Hi ?Dawn;
You are not going to like what I say, but it is the truth.
A badly behaved dog is the result of the way it is raised and trained.
Some people teach their dog to be mean, thinking that is the only way to have a good watch dog.
Others are so sweet to their dog and never says no to it, much less disclipline it.
A dog, like a human child has to be taught properly if they are to grow up right.
Spoiled children will hit their parents, and if they get away with it, they go further.
Putting him on a chain will only make him more aggressive.
You can be very sweet and kind to them, and you should be, but you also have to train them in the proper way to behave, or they will behave in a wild way.
Petsmart and Petco stores have weekend obedience classes where the owner handles the dog and learns the proper commands to givew to teach the dog well.
You will get as much out of the classes as the dog does.
You will learn how to be firm with them, and how to teach them to not be aggressive.
Sometimes, people can be too kind, and although meaning well, they can go the wrong way with raising an animal.
Man's Best Friend also has these group classes.
You could go and talk with the trainers there and I recommend you seriously getting into a class with your dog, as soon as possible.
It makes life so much easier when you have a well trained and well behaved friens and companion.
Charlotte