aggressive dog

Question
we have a 2 yo female boxer x collie. for the last 12 months or so she has been very aggressive towards our 9 yo female cocker spaniel, on two of these occassions we could only get her off by use of a check chain. there seems to be no rhyme nor reason for these attacks, but she seems worse when in season.  we plan to have her desexed, but didnt want to add more stress to the situation.  we have tried homiopathic drops which worked well for a while, but seem to have lost their effect. generally we can spot the behaviour that leads up to an attack and seperate them before something happens, but we feel like we're walking a tight-rope.  she also goes crazy if we try to put a harness & leash on her & she wont leave our yard for anything. she has never shown any type of aggression towards  people & adores our kids.  she is quite nervous of anyone she doesnt know.  we love her dearly but just dont know what to do.  our beautiful old cocker is the most gentle, loving creature who doesnt deserve to be hurt. we would appreciate any thoughts you may have.

Answer
I don't feel this is something that can be easily addressed via email.  I would suggest you locate a trainer in your area who is skilled in aggression and have them work with you and the dogs.  You can find someone by going to:

www.apdt.com and searching by city, state, zip code, etc.

I do feel, though, that altering (spaying, neutering) is a very good first step in eliminating any conflicts that are due to hormonal issues.