I was thinking that it would be really helpful to be able to toggle which borders are displayed in the designer. For example, it would be nice to only display just view-only borders when adding them in, but to hide them when working on default borders. To clarify, I envision an option to hide each type of border: default, attack-only, artillery, fortify-only and view-only. It also might be useful to hide one-way and two-way borders (so that you can work exclusively on one or the other if you'd like).

Yes.  It the big games the borders get to be a mess in a hurry.

+1

+1