Poor boy, and poor you worrying about him. I know the conventional training wisdom is to not make a big deal when you leave and return, but I'm wondering if some sort of greeting would help. Try using keywords and phrases indicating that you will return. When you come home, greet him warmly, tell him he was a good boy, and give him a yummy treat.
Put a tshirt you have worn into his bed for snuggling while you are gone.
Maybe put an open crate in his hallway area (not too close to the gate so he won't use it to try to get over the gate). If it is a wire crate, cover the top with another one of your tshirts.
Definitely work on exercise and tiring him out. My boys are suffering too from having their activity curtailed by weather, so I know how rough this is.
Having a companion dog sometimes helps, but not always. Some people have to resort to daycare.
I hope you can find the solution for your little guy.
__________________ Kristin, Max and Teddy |