Even though its not a breed problem, you may want to have his hearing and his eyesight checked. Sometimes when I come up on the Pyrs unexpectedly, they will challenge me until they realize that it is me. Also I am usually saying something to them so that they recognize that it is me. So if they arent "seeing" me so clearly, then they are certainly hearing me and they immediatly settle down. The only exception I had to this scenario was a dearly beloved mix breed who I had for 16 years, as she got older she could neither see as well or hear as well and I came close several times to getting bit. He is really a pretty dog.