How to make a legend with multiple map contours

I'm trying to create a legend from multiple contours (they come from different data so they have to be contoured separately). The problem is i'm plotting these contours on a map using contourm and when I try to get the legend it's giving the coast line and latitude/longitude lines as the legend lines.

I'm only comparing one contour from 4 different data sets, this is what I have so far:

 worldmap 'Asia'
 geoshow('landareas.shp', 'Facecolor', [1 1 1])
 contourm(laty, lonx, cors1, [1/exp(1)], 'b')
 contourm(laty, lonx, cors5, [1/exp(1)], 'r')
 contourm(laty, lonx, cors10, [1/exp(1), 'g')
 contourm(laty, lonx, cors10, [1/exp(1), 'k')

 legend('1-year average','5-year average','10-year average','20-year average')

Is there any way to set the tags for the contours and/or do them manually?

Thanks, Taylor