My one year old border collie, Oliver, has recently started some resource guarding, mostly with toys and his crate. He has two sisters and he never does it to them. I care for other peoples’ dogs and he’s fine with the girls, but when we have any boys here, he thinks he has to protect his toys and his crate, and sometimes anything he views as a resource. For instance, I’ll have him in his crate and a male dog will walk near the crate for no reason other than to grab a toy or just walk by, and Oliver will snarl and lunge at him for being too close. He’s caused one little scuffle from guarding the front door, and he’s also done this with toys and even the same grass they tried to eat lol. This is very new behavior from him. He is fixed, but I wonder if I waited too long. He was a year old when i got him fixed. The dogs he is doing this with are dogs he has known for quite a while so idk what the sudden change was.