you have to be a special kind of retard to get blown by a demo on a capping point, really...
you have a CIRCLE are to cap, just put one model inside the circle and you are good.
also, as okw you can just spend 15 munis on the balanced salvo of nades (don't even start on the "b-b-but is commander only ability!1!1" because the worthy ones have them.)
But most good players use either the minimap or the tactical map for capping and harassing points that arent heavily defended. And even if you suspect there's a demo but you have to cap the point anyway you can get wiped if you have to retreat because of the given retreat path. It usually doesn't even matter if the demo is exactly on the retreat path because it has such insane AOE. If you think it's fine you haven't played enough games vs Soviets.