Need help with dog aggression..

My gyp is not in heat. I wasnt home when the fight started, my mom and little siblings were over while i ran out for a few. My cur is nowhere near dominant and up until today they had a couple spats just showing who was dominant. My bulldog is not the top dog on the yard im just wondering if them being so close in age and neither being cut is my problem. My son got out into the yard while i was "educating" my bulldog and checking the cur, he walked right up to the pen i put him in before i even knew he was out there and was petting him with no problems. Of course being a parent that is always in the front of my mind.. But id really like to try everything to save the dog first..