I have a chocolate mint, currently in a container. I have a small patch of soil surrounded on four sides and am thinking about moving the mint to there, but I do not want it to escape into the lawn. Three sides do not concern me, but on the fouth side the space is bordered by a narrow cement walkway. How wide would the walkway need to be to keep the mint from invading the lawn via runners?
I would firmly suggest that you source either a thick plastic pot of large size, a 5 gallon bucket, a section of pipe, or a chunk of pond liner (EPDM rubber) and sink it into the ground surrounding your mint on all sides (you can cut the bottom out of the pot) with 3-4 inches (75-100 mm) aboveground and 12-20 inches belowground.
I love mint, but I regret planting it in my garden without firm containment. I have certainly seen runners more than 2 feet long, though I don't have an exactly analogous situation with a paved path - but I would not care to bet on it serving as containment. It's now firmly a part of the pantheon of weeds here.