I don't feel this is a tantrum behavior. Chi's are notoriously hard to house break. Mine is 11 and still will pee inside on a whim. We have a dog door so he always has outside access. Sometimes he'll pee right by the door. He gets walked regularly and he's with me most of the day. (We do nap together) and sleep together at nite.
We have 2 Chis, both male. The other one NEVE has an accident and will actually show me where the littler guy has peed. We are now entirely tiled through out the house but the pee-er will find a bath mat or a chair or whatever. I have no solutions but a tantrum, don't buy it. Look around on line or consult a dog behaviorist maybe that will help. I think it may be an insecurity. This guy was rescued from 2 homeless people living in a car. I think separation is very negative as a reaction to this problem and will just increase the dogs anxiety. Good luck
