Our dog of 3 yrs (German shorthair/black lab mix) has taken on biting people who come on our property. He is in an invisible fence environment and has now started biting people including kids that he has been aroundand played with him in his yard. He is not neutered which are considering doing, but not going to if we have to put him to sleep. Any chances this behaviour will change or does he have to be put down.
I do not know if the behavior will change if you neuter him but that would be the first thing I would do. I also recommend that you call in a specailist in dog training. Good luck, vetcare