I have a 4 year old lab/greyhound mix. I have had him since he was 3 month old. Everytime I leave the house he shakes like crazy. When he was really little- I crate trained him and everytime I would leave he would crap all over his cage. It has been 4 years and he still shakes and pants. I have a second dog- thinking that this would help and it hasn’t. What can I do???