Noah, our 1.5 yrs old male border collie mix, that was rescued in last Nov, has an aggression issue toward other dogs when they get too close to him. He shows his teeth and tries to tell them not to get any closer. He snaps and sometimes bites if they get too close (especially big dogs). We adopted Noah from a border collie foster family that had taken him because he had failed at the temperament evaluation test. He is a very sweet dog and he has been very gentle and nice to our 2 other dogs, Holly and Max, a 4 yrs old female border collie mix and even with 15 yrs old male German short hair pointer (who died recently). Noah and Holly are getting very well and play together a lot. He is very good with people even with little kids.
In March, we started taking him to training classes where there was an aggressive pit bull who barked and tried to lunge at him. We had attended 4 classes altogether before we finally pulled him out since it was such a chaotic class and we thought it was bad for Noah to stay any longer (I regret that we didn't withdraw sooner). Since then he developed an aggression. We have been working on his issue and will appreciate any advice. Thank you.