I have a 16 month old male Shepherd with whom I have inadvertently caused a big problem.

I have a 16 month old male Shepherd with whom I have inadvertently caused a big problem. When he was young he had hardly any interest in food and I tried everything to get him to eat, including teasing him that our other dog was, "going to get his food." I realize now how big a mistake that was. My question is, what can I do to undo the damage? To give you a little background, I am not an inexperienced dog trainer. I've raised many dogs, including two Dobermans that are well rounded, likable dogs and I used to show my Golden in obedience and took many first places with her on her way to her CDX. This GSD is a wonderful dog in every other way. I have spent much time with him, socializing, training and exercising him daily. He has never been allowed to go through a gate or door without me telling him it is ok. His stay is solid, his recall is great. He is a very nicely trained, very confident dog. He has never been people aggressive but just recently he had two incidents where he fought with another adult male dog. The latest was
with a Dalmatian that happened to be going for the same pile of horse poop that he was going for that someone was flinging. (We horse camp). He left a gash under the Dal's eye. After we separated them, I was on him and was able to hold his head to the ground until he gave in and would not hold my gaze. It was a frightening experience for all involved. The other incident was different. A friend has a Heeler that likes to bite the balls of other
intact males. My guy remembered this and went after him. All involved thought this was a justified reaction but when my GSD fights he is out for blood. I feel like an idiot for having contributed to such a problem with the food thing. Of course first thought is to have him neutered but what else can I do to nip this fighting thing in the bud? I had previously, extensively surfed your sight and instantly thought that maybe you would have an answer for me. I bought two of your tapes and enjoyed and learned from them both. Do you have
any suggestions For this problem? I am willing to use a shock collar and I am capable of giving a "10" correction.

Thanks,
Dennise