Making an object unclickable

How is it possible to make a game object unclickable?

What is happening is that my skybox is interfering with clicking objects in a scene when I am in a top-down camera. Somehow it seems to be absorbing the clicks. How can I make it 'ignore' the clicks?

You probably shouldn't be using a collider for a skybox, so this wouldn't be an issue, but in those cases where it's unavoidable, put the object on the IgnoreRaycast layer, and it will be invisible to mouse clicks.