There’s little need for eminent domain and in the case of building a wall or fence I see no need to steal land from anyone other than maybe 4’ at their fence lines. As a fence is needed simply place the fence as expediently as possible along standing properly lines. If that fences some people into a no mans land or even Mexico then that’s the way it must be. Offer them the option of fencing off which ever properly line they negotiate as appropriate. Then change the immigration law to allow them free passage through their section of fence and position a CBP Officer in a little gate house for them. In their down time they can monitor tv screens of drone footage of their area. It doesn’t have to be down the border in a straight line.