I agree with everything people have already suggested. I am new to the board, but what I have seen of 'red's posts, she seems very very knowledgable, and I would trust whatever she says.
My rotty was one of 13. All of his siblings are dead now, a few died in the whelping box, the rest were put to sleep for various reasons related to 'aggression'. When we got our baby he was just a little pup, but he was a little DEVIL. He had been alone with his little sisters (the parents both abandoned the litter and he was the only boy) and he basically spent his days alpha bossing them all around. When we got him he was a little grump and things only got worse as he got older. We were terrified just like you are, and desperate...wi lling to do whatever was needed. We immediately began crate training, and we got a book called 'Leader of the Pack' that book covers 10 or so things that dogs see as signs of who is the boss in the pack. If a few of those things are conflicting, the dog will be scared and try to gain alpha position. Let me give an example. Alphas eat 'best and first' (in a pack the dogs eat under VERY established/strict guidelines according to their place in the pack with the alpha male and female eating the first food, and the best parts of the kill. Then the other dogs eat next, in order of their status. Another biggie is that Alpha's control all possesions. A subordinate dog would NEVER EVER take a toy (in the wild a bone or prized find) that didn't belong to them, they would know that the Alpha controlled and doled out treats. I'll give you a third example. The alpha is the first one to check out something new, and would be the first in line coming out of the den.
Now if you have a domestic dog (they are domestic but still 100% follow wild dog law) and you give him treats or feed him before the family has dinner, and if you let him go out a door ahead of you...he has been signaled that he is the alpha because ONLY an alpha would have these privaleges.
If your dog is agressive towards anyone and there is nothing medically wrong, that tells you that the dog is thinking it is the boss, as alpha he has the right to make decisions about who to bite. All you should have to do to correct the problem (I say should because there could be some unrelated random weird thing I don't know about) is explain to the dog that it is NOT the alpha and that in fact it isnt the alpha even over caterpillers. This is a huge relief to any dog because it takes the responsibility off their shoulders and makes them feel safe. They learn that they have a competant, strong alpha and that they can just lay around and get loved up.
So what you do is you 'explain' in doggy language that you are now in charge and you are a loving, calm, assertive, powerful, safe alpha. Get that book if you can, it goes over the different things that cue the dog that you are alpha, and if you cant find it or for whatever reason cant get it, let me know and I will highlight the list of the different 'cues'.
This approach worked MIRACLES on my beast. He is the most loving happy tolerant waste of guard dog space you can imagine. I love him and he loves his position on the bottom rung of our ladder.
Ronda- I really hope this helps.