My sheltie is now three years old. Hasn't changed his behavior since he was a puppy. People come into the house and he wants to attack them until they sit down . Then forget if they get up to leave he tries to go after there heels ,so now know I now to hold him if they get up to leave. He barks constantly at the neighbors outside , people going by . And forget it if he hears the mailman coming down the road in his truck. Sometimes he will nip us if we tend to correct him when he is barking too much . It's like he is the boss . We have tried all the bells and whistles, water spray, coins in a can, I have tried four different no bark collar. They work at first and then it' s like he don't mind. I' ve tried li- the amine, melatonine nothing seems to calm this dog down. And yet there are times when he. can be so lovable.