Thanks for all the comments. It's been a few years since I have built anything for the yard for Christmas. My original plan was to make Snoopy and Chuck out of 'Monster Mud' which is a chicken wire form wrapped in burlap that has been covered in a wallboard compound/paint mixture.It sounds like it would fall apart when it gets but holds up really well, and when dry is extremely hard. I have a couple of props that are six years old and are just now needing a little touch up.
But because of time I ended up using the 2 inch foam board. There's two types of insulation board commonly found at Home Depot and Lowes: Extruded and Expanded the expanded is the kind typically used as packaging in boxes. It's white and made from little balls of Styrofoam, when broken it leaves little foam granules everywhere. The Extruded is the best foam to use if you can find it, usually blue or pink, the pink being a little harder than the blue. The extruded foam is really what you want to use because of its much smoother texture and its increased hardness. Around here a 4x8 sheet of 2 inch foam runs about $20.
As far as cutting it, I use mainly all of my woodworking tools. I do have a wonder cutter from http://hotwirefoamfactory.com/home.phpfor the really fine cuts.The jigsaw works fine for cutting out the shapes, and you can use a small saw for the small cuts like the ones in Woodstock's head. I use the circular saw to cut the full-sized sheets down to more manageable sizes. The only drawback is that the foam particles stick to everything more than normal sawdust, and you need to where a dust mask since the foamdust is not good for you. If you do use a foam cutting tool do it in a well ventilated area since melting foam fumes are toxic.
Painting foam is not too bad.I stay away from anything in a spray can. I know they have floral spay paintfor foam but it is pretty expensive here so I don't use it. I use exterior latex house paint for most of the large areas (Snoopy, the doghouse) and then the Acrylic craft paint from Wall Mart or Michaels for the rest of the areas. I may put on a clear finish I have some which helps protect it from scratches, if I don't have any they go out once the paint has dried for about 24 hours. So far I haven't had any problems, most scratches are so small nobody besides myself are going to notice them especially at night. I have tombstones that are 6 years old and just touched up some this year, mainly because stuff has fallen on them or I when I put them in storage I put something heavy on them. Of course we don't have snow in NC, just the cold air.
I will actually get a some instructions together and posted. I have a few pictures here http://christmas.kreepyhollow.com/Pictures.htmI have more to add today.