Blood-Thirsty

Question
My 6 year old full-blooded male boxer was on our property when a stray male dog came up to our back porch. He attacked it and caused it to have to be put to sleep.  Is this a dogs nature or do I need to be worried about future attacks?  Especially with my children.  He has never been vicious or anything of the sort.  He is "A Big Baby"  Is it true that once they get the taste of blood, they will thirst for it?  My neighbors don't "trust" him anymore so everytime I take him outside, he has to be tied up.  I feel like he isn't getting the exercise that he is used to.  He has never been tied up.  Will this make him meaner?

Answer
Determining whether this is your "dog's nature" would be extremely difficult without being there to observe his behaviors.

Is your dog neutered?  Was the other dog neutered?  Two un-neutered males can often lead to fights.
If your dog is not neutered, taking care of this would eliminate one factor.  Dogs can be very protective of their property, and unaltered animals even more so.

I do not believe dogs develop a taste for blood.

You indicate that you now have to tie him up outside.  What was the procedure before?  Did he run loose in the neighborhood, or do you have a fenced yard?

Letting a dog run loose is not only dangerous to the dog (as in getting hit by a car) but is also not being a responsible dog owner.

If you are concerned about his getting enough exercise, taking him for leashed walks is a good solution.

Showing your neighbors that you are doing whatever you need to do in order to be a responsible dog owner and a good neighbor (neutering the dog, containing him to his own property, taking him to obedience classes) would go a long way toward helping them trust the dog again.