Feature request improvement to "(Visible only on mouseover)"

I'd like to increase the size of the hitbox for an invisible fence, so that you don't need to have the mouse directly over it to see it. Ideally I could make the hitbox the entire left side of my screen, if the mouse is there then my invisible fence could become slightly visible. It would be cool if the fence faded in proportion to the proximity of the mouse - for a smallish invisible fence this would make it a lot easier to find.