We have those cords too, and while I realize that the best thing would be to replace all the blinds, we just don't have that money right now.
So, what we do (and I know it gets cumbersome, but that's just the way it has to be) is to get up on a chair every time we raise or lower the blind and secure the cord up high--out of DS's reach. In other words, either drape it over a curtain rod or twist it around a nail or hook we've fastened high up on the wall.
I know it's not foolproof, and it does get tiring, but the way I see it--the point is to get the cord out of his reach, right? We just have to be really vigilant about actually keeping the cords out of his reach.
I will be following this thread for other ideas as well, as this is something we are concerned about. Maybe someone else has good ideas.