Is the dog I do daycare for becoming possessive of my house or me?

I always start right away with a nice long walk sometimes starting with the new dogs on the opposite side of me before walking them on the same side about ten minutes or so into the walk just depends on the dog. That gets some energy out and bonds everyone and establishes your authority. That doesn't always immediately carry over to behavior inside the house though. If that is the case, I keep everyone calm for awhile and go on another walk before allowing excitement and playing. All just based on the dogs! It doesn't sound like this dog is truly aggressive so it's good practice in case you get a tougher case!

It does sound like he's getting a little territorial. This happens and if the dog is just a bit jealous or territorial it's fairly easy to remedy. What Kellyn does with walking them together I've found to work really well a lot of times. However, I tend to get quite a few shy dogs so I have gates that separate one area of the house from another. If one of the dogs is not immediately friendly and you can't or don't want to risk a walk right away, just keep them separate for a while. If it's a gate separating them where they can sniff that's usually helpful. I have some dogs that can immediately hang out with others, some that need a few minutes, and some that need a few days to feel comfortable. Good luck!

I do all initial meetings between dogs, my own as well as any client's dogs who are with me at the time a dog is dropped off, outside in my yard. Thankfully, I have a fenced in yard so it makes the meetings go much easier. I do this no matter how long the dogs have known each other. This has seemed to alleviate any issues with them.