What does he's like a dog marking his territory?

The phrase "he's like a dog marking his territory" suggests that someone is being possessive or assertive in a way that signals ownership or control over a space or situation. It implies a certain level of dominance and the need to establish boundaries, similar to how a dog marks its environment to communicate its presence to others. This behavior can be seen as both instinctual and a reflection of insecurity or a desire for validation.