First off........
As far as your question goes....it isn't about him "seeing" the does, but smelling them. The closer they are, the more likely he is to find a way to them.....so, it depends on your setup, space, size and breed of goats.....there is a huge difference between a nigerian dwarf and a kiko.....but, no matter the breed ya sure want more than a fence between them....
I was told out of sight and smell. Even a plywood fence if they can't see each other definitely helps. Soon enough I'm going to be in your shoes and will learn as I go..