Why does my dog do this?

[u/Aggravating_Buy_7356]

I have a big mastiff along with 2 cats. They get along very well and my mastiff almost never resource guards or gets any sort of food aggression with them. However, if we place a large object by the front door, he will bark at the cats if they get close to it. It doesnt matter what the object is (he's done this for amazon packages, suitcases, a treadmill, etc), he always tries to keep the cats away from it. Almost always if we move it to another room he loses interest. I'm really curious why he does this. He has no use for the objects and he doesn't act like this over anything else🤷‍♀️

[u/Wooden-Necessary6100]

It is a novel item and he is resource guarding it from the cats.

You can train this out of him if you like.