FWIW...I used Liquid Nails to glue the 1" boards in place, already pre-cut to approximate the hill I wanted to create. Then after they were dry, I finished cutting away with an Xacto the foam board I didn't want and also was able to cut a sloping hill where needed without too much fuss. Of course, the danger is, if you cut wrong...it's already glued in place and harder to work around. Also, I tried not to get too smooth an edge on the cut foam board so that the result would look like a hill that had some grading work done to it (sorta like what highway departments do to hill sides near roads). The imperfections (textures) made when you pre-score then break apart the foam board resembles an escavated hillside when you paint it.