These Four Walls

No, not the song.  I'm talking about the four walls of my produce warehouse.  My mission for the weekend was to get the two removable walls framed up - mission accomplished.  I haven't quite figure out how to hold them in place yet.  I'm thinking some sort of pin or peg that will go into holes drilled into the floor.  Whatever I come up with, it needs to be easy to remove the walls, but they also need to stay firmly in place when the building is assembled.