I have a 200' thin rope I keep with my practice basket. It's got marks every 5 feet out to 50, then every 25 feet out to 200'. I can only measure distances for shorter approaches and long putts, but it is convenient. I've thought about getting a longer rope, I just already had this one and am too lazy to do all the measuring again.
Why don't you measure out to 200 feet, stick it in the ground, walk back and grab the other end, walk it out to 400 feet, then you know the lengths from 200 to 400.