The Grass Doctor

How to edge between two different types of grass? I am working on landscaping my yard. In order to conserve water, we are using a local drought resistant types of grass. There will be a large (probably 30'x60') play area, featuring a grass with a long green season called Reveille. The rest of the lawn will be planted with a different type of grass which has a shorter green season called Legacy Buffalo grass. I am trying to determine how to create a border between the two grasses, so that they do not blend together. I want it to look natural. Any suggestions?

Is all Buffalo Grass naturally pollen-free? Or is it only the designer stuff like Legacy®. Legacy® is sold as "essentially pollen-free" and is recommended by horticulturist Thomas Ogren. I was just wondering if its characteristics are typical of Buffalo Grass or if it is unique.